BIOLOGY
APR , ,2?b
'
^eM^/vc . 2J^f^ ^^^^
The person charging th.s ma enaH re^
sponsible for its return to the library ^"-o^
which it was withdrawn on or betore the
Latest Date stamped below.
for dUtlpllnary action and may
the University. ^
Li61_O-10<)6
THE GIANT PANDA
A MORPHOLOGICAL STUDY
OF EVOLUTIONARY MECHANISMS
D. DWIGHT DAVIS
M'-
''y^
^'^PU
"'//:
^r
^
FIELDIANA: ZOOLOGY MEMOIRS
VOLUME 3
Published by
CHICAGO NATURAL HISTORY MUSEUM
DECEMBER 7, 1964
t-L-i)
Ob
FIELDIANA: ZOOLOGY MEMOIRS
VOLUME 3
NATURAL HISTORY"
MUSEUM
lTllU;H!f V l"i ! !l ^ HOTWmilll . I
CHICAGO NATURAL HISTORY MUSEUM
CHICAGO, U.S.A.
1964
I/. 3
Cop''?
THE GIANT PANDA
A MORPHOLOGICAL STUDY OF EVOLUTIONARY MECHANISMS
Photograph by Waldemar Meisler
THE GIANT PANDA MEI LAN
Chicago Zoological Park, September, 1952
THE GIANT PANDA
A MORPHOLOGICAL STUDY
OF EVOLUTIONARY MECHANISMS
D. DWIGHT DAVIS
Curator, Division of Vertebrate Anatomy
FIELD lANA: ZOOLOGY MEMOIRS
VOLUME 3
Published by
CHICAGO NATURAL HISTORY MUSEUM
DECEMBER 7, 1964
"The field of macrotaxonomy ... is not directly accessible to the geneticist . . .
Here the paleontologist, the comparative anatomist, and the embryologist
are supreme."
Richard Goldschmidt
Edited by Lillian A. Ross
Patricia M. Williams
Edward G. Nash
Publication costs defrayed in part by National Science Foundation
Grant GN-116
Library of Congress Catalog Card Number: 6i-8995
PRINTED IN THE UNITED STATES OF AMERICA
BV CHICAGO NATURAL HISTORY MUSEUM PRESS
6fO
a ^3 J f
S' ' ^'
r
PREFACE
This study of the anatomy of the giant panda
was originally intended to determine the taxo-
nomic position of this species. As the dissection
progressed, other questions of rather broader in-
terest developed, and the scope was widened to
embrace them.
In studies of this kind the customary procedure
is to compare structures with those of supposedly
related organisms, and estimate relationships of
organisms from these comparisons. In the back-
ground are the broader questions of the phylogeny
and fundamental uniformity of vertebrate struc-
tures, which have long been the core problems of
comparative anatomy. But superimposed on the
underlying pattern of uniformity there is a be-
wildering array of differences, mostly adaptations
to special ways of life. Phylogeny continuity of
ancestry explains the uniformities in vertebrate
structure. It cannot explain the differences, which
represent the active creative aspect of evolution.
Yet we cannot pretend to explain the history of
vertebrate structure without rational theories to
account for the differences as well as the uni-
formities.
The existence of an underlying uniformity in
vertebrate structure is now so well documented
that it is practically axiomatic, but comparative
anatomists have scarcely begun to seek similarly
adequate explanations for the differences in verte-
brate structure. At this stage I believe it is of
crucial importance to ask whether comparative
anatomy can undertake to explain, in causal-ana-
lytical terms, the structural differences that char-
acterize taxa among vertebrates. If it cannot, then
I would agree with the statement once made by
D. M. S. Watson, that comparative anatomy is a
term "now obsolescent."
Such an extension of the goal of comparative
anatomy assumes that the genetic backgrounds for
the kind of morphological differences with which
anatomists are concerned are so simple that they
can be estimated with reasonable certainty by in-
ferring causes from results, without resort to breed-
ing experiments. For some of the primary differ-
ences at the generic level this appears to be true.
Evidence is steadily accumulating that, in verte-
brates, a quite simple change in epigenetic mecha-
isms may have a profound and extensively different
end result. Moreover, the result is an integrated
oi'ganism. This suggests that in favorable cases,
and at low taxonomic levels, the comparative anat-
omist may properly seek the mechanisms behind
the differences he observes.
In many ways the giant panda seems to be al-
most ideally suited to a test of this thesis. I do
not, of course, believe that I have explained com-
pletely how the morphology of the giant panda
arose from the morphology of the bears, or that
everyone will accept my interpretations. I ask
only that this study be regarded as a first approxi-
mation, a first attempt to explain the structural
differences between a derived and an ancestral
organism in terms of causal mechanisms, an at-
tempt to identify the raw materials on which
natural selection acted.
I am indebted to several institutions and in-
numerable individuals for assistance in this study.
On several occasions the United States National
Museum allowed me to study skeletons housed
there, and lent embalmed and osteological mate-
rials for detailed study in Chicago. The American
Museum of Natural History and Carnegie Mu-
seum permitted me to study and measure skeletons
in their collections. Much of the material on
which the woi-k was based, including all the em-
balmed giant panda material, originally came from
the Chicago Zoological Park. Observations on liv-
ing carnivores were made at both the Chicago Zoo-
logical Park and the Lincoln Park Zoo.
Over the years so many individuals have con-
tributed to this study in various ways that it is
impossible to thank them individually. I have
profited particularly from numerous discussions
with Dr. Harry Sicher, Dr. E. Lloyd DuBrul, Dr.
Rainer Zangerl, Pi'ofessor Bryan Patterson, and
Dr. Carl Cans. Dr. Zangerl made many X-ray pho-
tographs for me. My late colleague. Dr. Karl P.
Schmidt, repeatedly interrupted his own work to
help me translate difficult German passages.
In a work of this kind the artist tends to become
almost a collaborator. I have been particularly
fortunate in the several artists who worked with
6 PREFACE
me from time to time: the late John C. Hansen, of the finer blood vessels and nerves in addition to
who made most of the bone drawings; John J. making most of the drawings of the soft anatomy;
Janacek; Miss H. E. Story, who dissected out most Miss Phyllis Wade; and Mrs. Edward Levin.
D. D. D.
CONTENTS
PAGE
List of Tables 9
Introduction 11
Goals and Methods of Comparative Anatomy 11
Material and Methods 13
History 14
Distribution 17
Habits and Behavior 20
External Characters 28
Description 28
Measurements 31
Growth 31
Proportions 31
Conclusions 40
Skeleton 41
The Skeleton as a Whole 42
Measurements 44
The Skull 46
The Skull as a Whole 47
Cranial Sutures and Bones of the Skull 62
Hyoid 64
Review of the Skull 65
Summary of Skull 74
The Vertebral Column 74
The Vertebral Column as a Whole 74
Descriptions of Vertebrae 78
Review of the Vertebral Column 84
Conclusions 85
The Thorax 85
Ribs 85
Sternum 87
Review of the Thorax 88
The Fore Leg 88
Bones of the Fore Leg 88
Review of the Fore Leg 100
The Hind Leg 102
Bones of the Hind Leg 102
Review of the Hind Leg 120
7
8 FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
PAGE
Discussion of Osteological Characters 122
Conclusions 124
Dentition 125
Description 125
Discussion of Dentition 127
Conclusions 130
Articulations 131
Articulations of the Head 131
Articulations of the Fore Leg 132
Articulations of the Hind Leg 140
Review of Joints 145
Muscular System 146
Muscles of the Head 149
Muscles of the Body 158
Muscles of the Fore Leg 172
Muscles of the Hind Leg 183
Discussion of Muscular System 196
Conclusions 198
Alimentary System 199
Mouth 199
Salivary Glands 199
Tongue 202
Pharynx and Esophagus 204
Stomach 207
Intestines and Mesentery 208
Liver and Gall Bladder 212
Pancreas and Spleen 215
Discussion of Digestive System 216
Conclusions 218
Urogenital System 219
Urinary Organs 219
Male Reproductive Organs 221
Female Reproductive Organs 225
Discussion of Reproductive Organs 225
Conclusions 228
Respiratory System 229
Larynx 229
Trachea 235
Lungs 236
Conclusions 237
Circulatory System 238
Heart 238
Arteries 245
Veins 280
CONTENTS 9
PAGE
Ductless Glands 288
Hypophysis 288
Thyroid 288
Parathyroid Bodies 288
Thymus 288
Nervous System 289
Brain 289
Discussion of Brain 297
Cranial Nerves 298
Cervical Plexus 305
Nerves of the Fore Limb 306
Thoracic Nerves 310
Nerves of the Hind Limb 311
Sympathetic System 315
Special Sense Organs 317
Eye 317
Middle Ear 318
Comparative Anatomy and evolution An Evaluation of the Test Problem
The Relationships of Ailuropoda 322
Morphogenetic Mechanisms in the Evolution of Ailuropoda 323
Conclusions 326
References 328
Index 335
LIST OF NUMBERED TABLES
PAGE
1. Limb segment ratios in carnivores 35
2. Limb proportions in carnivores 36
3. Weight in grams of dry skeleton 42
4. Weight ratios in dry postcranial skeleton 43
5. Surface areas of limb bones 43
6. Measurements of carnivore skeletons 45
7. Cranial capacity of carnivores 46
8. Skull proportions in generalized and specialized carnivores 66
9. Vertebral counts in carnivores 75
10. Relative proportions of divisions of the vertebral column in carnivores 75
11. Measurements and indexes of pelvis in carnivores 103
12. Relative mass of masticatory musculature 154
10 FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
PAGE
13. Relative weights of masticatory muscles in carnivores 155
14. Relative weights of muscles of the shoulder and arm in carnivores 183
15. Relative weights of muscles of the hip and thigh in carnivores 195
16. Myological characters in arctoid carnivores 197
17. Intestinal length in arctoid carnivores 210
18. Liver weight in mammals 214
19. Percentage differences from control animals in gut measurements of pigs raised on herbivorous
and carnivorous diets 217
20. Number of renculi composing kidney in bears 220
21. Dimensions and proportions of kidneys in arctoid carnivores 220
22. Kidney weights in mammals 221
23. Heart structure in arctoid carnivores 243
24. Branches of aortic arch in arctoid carnivores 277
25. Composition of lumbosacral plexus in carnivores 315
INTRODUCTION
It is my intent to make this study a test, based
on the anatomy of the giant panda, of whether the
comparative method can yield information that
goes beyond the customary goals of comparative
anatomy. It is evident, to me at least, that more
than fifty years ago comparative anatomy reached
a stalemate that can be broken only by seeking
answers to new and different questions. I believe
it must shift its major emphasis from the conserva-
tive features of evolution to its radical features,
from the features that organisms under compari-
son have in common to those they do not have in
common. It must seek rational explanations for
these differences, drawing on data from other fields
where this is necessary and possible. In this study
of the giant panda the structural differences be-
tween it and the bears, and the ways in which these
differences arose, will be our primary concern.
The original problem that motivated the work
the proper taxonomic position of Ailuropoda was
soon settled; Ailuropoda is a bear and therefore
belongs in the family Ursidae.' The further prob-
lem of attempting to infer the causal mechanisms
involved in the origin of Ailuropoda from its ursid
ancestors requires some discussion of goals and
methods.
GOALS AND METHODS OF
COMPARATIVE ANATOMY
The classical goal of comparative anatomy was
to demonstrate the existence of an essential and
permeating uniformity or "ordering" in the struc-
ture of vertebrates. This goal has been reached.
Details of the picture remain to be filled in, but
the unifying concept itself is now so well docu-
mented that it is no longer open to serious debate.
Phylogeny, the genetic relatedness of all verte-
brates, provides an explanation for the uniformity.
This aspect of the history of vertebrate structure
cannot be expected to give rise to further concepts.
> This conclusion is not based on one or a few characters,
but on a host of similarities, many of them subtle, through-
out the anatomy. I tried to present the data on the affinities
of Ailuropoda before going on to other considerations, but
this became so difficult that I gave it up. Therefore one of
the primary conclusions is assumed throughout the text.
We may well ask where comparative anatomy is to
go from here.
From the evolutionary standpoint the structural
differences among vertebrates are just as impor-
tant as the structural uniformities; these two are,
in fact, the obverse and reverse of the phylogenetic
picture of vertebrate structure. Years ago W. K.
Gregory distinguished them as "habitus" and "her-
itage" characters. We cannot claim to have ex-
plained the particular structure of an organism if
we explain only its heritage characters and offer no
explanation for its habitus characters. An "expla-
nation" must account for the differences in terms of
evolutionary mechanisms, not merely relate them
to the functional requirements of the organism
in other words, explain them in the same causal
sense that common ancestry explains the heritage
characters.
Classical comparative anatomy tended to con-
centrate on the major features of vertebrate struc-
ture the differences that characterize orders and
moi-e often classes. Such, for example, are the
homologies of the gill arch derivatives, of the ele-
ments of the mammalian middle ear, of the cranio-
mandibular muscles. There was practically no in-
terest in how and why such changes came about,
and the morphogenetic and selective mechanisms
involved in these massive alterations are prob-
ably irretrievably lost in the vast reaches of time
anyway.
Structural differences at about the generic level
are usually far less profound and more recently
evolved, yet they often represent a level of mor-
phological differentiation to which the methods of
comparative anatomy can be applied. In this re-
spect they differ from the characters with which
the geneticist customarily deals. At about the
generic level we may hope to decipher the mech-
anisms responsible for the observed differences in
structure between two or more related forms. A
procedure designed to yield such information is
followed in this study. The procedure may be
divided into a series of steps. These are:
(1) Identification of the structural differences
between Ailuropoda and its structural ancestor,
Ursus. At the outset nothing was known of pos-
11
12
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
sible pleiotropic effects, allometric relationships,
morphogenetic patterns, or obscure functional re-
lationships. Therefore all differences were tabu-
lated uncritically, without attempting to evaluate
them. For the same reason the entire anatomy
of the organism was covered so far as practicable.
(2) Correlation of the observed structural differ-
ences between Ailuropoda and Ursus with dif-
ferences in habits or behavior. This is the first
step in sorting out the adaptive features peculiar
to the anatomy of Ailuropoda features that pre-
sumably represent the modifications of the ursid
morphology resulting from natural selection. This
step results in two categories: (a) those differences
that can be correlated with differences in habits or
behavior, and (6) those that can not.
The differences in category b may be conspicu-
ous, and their presence must be accounted for.
They may be genetically related to an adaptive
modification but not themselves adaptive. They
may reflect the results of an inherited differential
growth rate, whereby the proportions of a mor-
phological unit may change with the absolute size
of the unit. A classical example of this effect is
the antlers of deer. They may merely reflect re-
laxed selection pressure on certain functions. The
decision as to whether a condition is or is not adap-
tive is often very difficult, requiring considerable
knowledge of mechanics and engineering, as well
as intimate knowledge of the habits and behavior
of the animal.
(3) Separation of the adaptive features that are
genetically determined from those that are only
indirectly related to the genetic substrate. Many
conspicuous features in the skeleton depend only
on the capacity of bone to respond to extrinsic
forces. Many soft tissues have a considerable ca-
pacity to accommodate their form to the molding
action of extrinsic forces. The caliber of blood
vessels varies with the demands of the tissues they
supply, even during the life of the individual; if
one kidney is removed, the remaining one hyper-
trophies. Such conditions are adaptive, but they
are not primary results of selection; they are the ex-
ogenous adaptations of Waddington (1953). They
reflect the action of natural selection at second or
third hand, so to speak. If we are seeking to iso-
late the structural features on which natural selec-
tion acted directly, these secondary and tertiary
effects must be discounted.
These three steps have presumably isolated the
morphological features in Ailuropoda that (1) dif-
fer from those in its structural ancestor, Ursus,
(2) are functionally correlated with differences in
habits and behavior, and (3) are genetically deter-
mined. They are the direct results of natural se-
lection in the step from bear to giant panda. As
will appear in the sequel, these features seem to be
surprisingly few; we are not interested here in
minor polishing effects, but only in decisive dif-
ferences. We do not yet know the materials on
which natural selection acted to effect these
changes. One final step remains:
(4) Determination of the morphogenetic mech-
anisms that were involved in effecting these
changes. This should be an experimental prob-
lem, but obviously experimentation is impossible
in the vast majority of cases, including this one.
Fotunately, morphogenetic processes appear to be
remarkably uniform among mammals. By a judi-
cious combination of the comparative method with
the known data of mammalian epigenetics I be-
lieve it is possible to infer, with varying degrees of
confidence, the true mechanisms behind many of
the major structural differences that distinguish
Ailuropoda from the true bears. Many of the
"unit characters" involved appear to be sizable
morphological units, although it does not neces-
sarily follow that the shift from bear condition to
panda condition was made in one jump, or that
such morphological units are controlled by simple
genes. It is clear, however, that they are geneti-
cally controlled as units. It would be futile to at-
tempt to reconstruct the history if major adaptive
differences represent accumulations of numerous
small mutation effects.
To the extent that these four steps are carried
out successfully, the differences between the giant
panda and the true bears will be explained rather
than simply described.
Almost without exception, students of the higher
taxonomic categories have been reluctant to believe
that the kinds of morphological differences they
observe represent accumulations of small muta-
tion effects such as the geneticist customarily deals
with. The once-popular solution invoking un-
known imminent forces to explain systemic differ-
ences is no longer common. Modern students
have sought genetic mechanisms capable of pro-
ducing phenotypic differences of the magnitude
they believed were involved. Goldschmidt (1940),
for example, emphasized (among other things) the
massive co-ordinated differences that can result
from acceleration and retardation of gene-con-
trolled developmental processes. Rensch (1960)
listed pleiotropy, allometric growth rates, and
compensatory correlations among the agents ac-
cessible to natural selection as capable of pro-
ducing extensive generalized effects on the organism
as a whole.
It is now generally recognized that gi'owth is es-
sentially a process of multiplication of cells. Multi-
DAVIS: THE GIANT PANDA
13
plicative rates differ in different parts of the body,
and in the same part at different times during its
growth period. Regional growth rates may inter-
fere with each other, resulting in negative interac-
tions and in extreme cases even in deformation of
the entire growth profile of the body. Correlation
studies show clearly that both regional and gen-
eral growth rates are genetically controlled as units.
These insights stem chiefly from Huxley's Prob-
lems of relative growth, which in turn grew out of
the earlier On growth and form of D'Arcy Thomp-
son and Goldschmidt's Physiologische Theorie der
Vererbung. They provide a mechanism capable of
producing plastic deformation of a common pat-
tern, which is what the comparative anatomist
seems to see when he compares homeomorphic or-
ganisms. A bridge between genetics and compara-
tive anatomy was sought in vain during the first
third of this century; it now seems to have been
found.
Partly because evolution is a cumulative and
non-repetitive process, and partly because growth
fields in vertebrates have proved refractory to ex-
perimental techniques, their role in the morphosis
of animal form has been deciphered almost exclu-
sively by morphological methods. The primary
tool is demonstration of correlations; the method
is comparative. Whether subtle correlations are
sought by sophisticated statistical methods (as in
recent studies of mammalian teeth) , or more obvi-
ous correlations by means of coarser but no less
rigorous comparative methods (as in the present
study), the goal is the same. It is to identify and
circumscribe the material bases for differences
among homeomorphic organisms. This is a proper
field for the comparative anatomist.
MATERIALS AND METHODS
This study is based largely on the embalmed
and injected body of a giant panda that lived in
the Chicago Zoological Park from February, 1937,
to April, 1938. The panda was popularly known
as Su Lin. Unless otherwise stated, all statements
relating to the soft anatomy are based on this
specimen. Su Lin was a subadult male (teeth fully
erupted). His age (estimated) was 16 months at
death. He was in excellent condition and weighed
132 pounds. Preserved portions of the carcass
(head, fore and hind limbs, heart, genitalia) and
the skeleton of an adult male giant panda (known
as Mei Lan) were available. Mei Lan was esti-
mated to be 15 years old at death. He was much
emaciated, and weighed 205 pounds after autopsy.
The following skeletal material of Ailuropoda
was available for detailed study:
CNHM 31128 id' ad.) Szechwan: Yehli. Complete skel-
eton.
CNHM 36758 ( 9 ad.) Szechwan: Dun Shih Goh. Com-
plete skeleton.
CNHM 34258 (- ad.) Szechwan: Mouping Dist. Skull,
lower fore legs, fore and hind feet.
CNHM 74269 ( (f ad.) (zoo animal: Mei Lan). Complete
skeleton.
CNHM 39514 (- ad.) Szechwan: Dun Shih Goh. Skull.
USNM 259076 ( 9 jv.) Szechwan: Wen Chuan. Skull.
USNM 259027 ( c? ad.) Szechwan: Wen Chuan. Pelvis.
USNM 259403 ( 9 ad.) Szechwan: Wen Chuan. Pelvis.
Most of the data on the soft anatomy of bears
came from the following captive animals that died
in the Chicago Zoological Park:
CNHM 48304 (d" ad.) Ursus thibetanus, embalmed and
injected body.
CNHM 49061 ( & juv.) Ursus americanus, embalmed and
injected body.
CNHM 57267 ( 9 ad.) Ursus americanus, embalmed head,
fore leg, and hind leg.
CNHM 57200 ( 9 ad.) Tremarctos ornatus, embalmed head,
fore leg, and hind leg.
The following bear skeletons were used for most
of the detailed osteological data:
CNHM 43744 (- ad.) Ursus ardos; Iraq.
CNHM 47419 (- ad.) Ursus arctos; Iraq.
CNHM 44725 (cf ad.) Ursus americanus; (zoo animal).
These three skeletons were supplemented with
numerous skeletons and partial skeletons of bears,
representing several genera and species, in the col-
lections of Chicago Natural History Museum.
Partial dissections were made of several procyo-
nids, all embalmed zoo animals, representing the
genera Procyon, Nasua, Bassariscus, Potos, and
Ailurus. Numerous skeletons of these genera, from
both wild-killed and zoo animals, were available.
Linear measurements up to 150 millimeters were
made with Vernier calipers graduated to 0.1 milli-
meter. Lengths beyond 150 millimeters were meas-
ured with large calipers and a meter stick. Weights
up to 2 kilograms were determined with a small
Ohaus triple beam balance. Larger objects were
weighed on a large Ohaus beam balance with a
capacity of 21 kilograms. In weighing preserved
soft tissues the usual precautions of removing ex-
cess surface liquid by blotting were taken.
HISTORY
The synonymy of Ailuropoda melanoleuca may
be summarized as follows :
Ailuropoda melanoleuca (David)
Ursus melanoleuciis David, 1869, Nouv. Arch. Mus. Hist.
Nat., Paris, Bull. 5, p. 13.
Ailuropoda melanoleuca Milne-Edwards, 1870, .\nn. Sci.
Nat., Paris, (5), Zool., 13, art. 10.
Pandarctos melanoleucus Gervais, 1870, Nouv. Arch. Mus.
Hist. Nat., Paris, 5, p. 161, footnote; 1875, Jour.
Zool., Paris, 6, p. 87.
Ailuropus melanoleucus Milne-Edwards, 1871, Nouv.
Arch. Mus. Hist. Nat., Paris, Bull. 7, p. 92.
Aeluropus melanoleucus Lydekker, 1891, in Flower and
Lydekker, Mammals living and extinct, pp. 560-561,
fig. 256.
During his stay in Mouping on the second of his
three expeditions to China, the noted French ex-
plorer and naturalist Pere Armand David learned
of the existence of a curious black and white "bear."
This animal, called pei-hsuing ("white bear") by
the natives, aroused David's interest, and he em-
ployed hunters to capture specimens of it for him.
After almost a month of unsuccessful hunting a
young female was brought to him on March 19,
1869, and two weeks later he acquired an adult of
the same sex. Although erroneously believing it
to be a bear, David immediately recognized the
animal as a novelty to science. He drew up a con-
cise but adequate description under the name Ur-
sus melanoleucus and despatched it to Alphonse
Milne-Edwards at the Paris Museum with an ex-
planatory note requesting its publication. David's
letter, which was duly published in the Nouvelles
Archives of the Paris Museum, introduced to sci-
ence the animal now known as the giant panda.
The subsequent history of the giant panda can best
be presented in chronological form.
1870. Milne-Edwards, after e.xamining David's
material, noted that its osteological characters and
dentition "clearly distinguish" the giant panda
from the bears and approach those of the lesser
panda and raccoons. He erected the genus Ailuro-
poda to receive it. Gervais, on the other hand,
concluded from a study of an intracranial cast that
its brain structure allies it to the bears. Gervais
considered it worthy of generic distinction, how-
ever, and proposed the name Pandarctos.
1871. David published a few brief notes on
the habits of the giant panda, and even today sur-
prisingly little can be added to these original ob-
servations. David recorded that it is restricted to
high altitudes, that it is herbivorous, and that it
does not hibernate. Only one of his statements
has not been substantiated : "It is said that it does
not refuse meat when the occasion presents itself;
and I even think that this is its principal nourish-
ment in winter."
Milne-Edwards, believing that the generic name
Ailuropoda was preoccupied by Gray's use of the
name Aeluropoda for his "Section I. Cat-footed
Carnivora" in the Catalogue of Carnivorous, Pachy-
dermatous and Edentate Mammalia in the British
Museum (1869, p. 3), proposed the name Ailuropus
for the giant panda.
1868-74. Milne-Edwards, in the Recherches des
Mammiferes, gave a detailed description of the
skin, skull, and dentition. His re-examination led
him to the conclusion that Ailuropus should be
placed between the bears and the [lesser] panda.
1875. Gervais, after an examination of the
skeleton of David's panda, reasserted his former
opinion that the giant panda is an aberrant bear.
1885. Mivart, in his careful review of the clas-
sification of the arctoid carnivores, concluded that
Ailurus is a procyonid and that Ailuropus is allied
to Ailurus and therefore is a procyonid, too. Mi-
vart thus set the pattern that, with few exceptions,
has been followed by British and American auth-
ors to the present day. His conclusion is based on
the usual agreement of skull architecture and den-
tal morphology that was to be stressed repeatedly
by later authors.
1891. Flower and Lydekker, in their Mammals
Living and Extinct, placed "Aeluropus" in the Ur-
sidae and "Aelurus" in the Procyonidae. Their
emendation of Milne-Edwards' generic name Ailu-
ropus, appearing in an authoritative work, resulted
in considerable confusion in subsequent literature.
1895. Winge regarded the giant panda as a
very close relative of the extinct Hyaenarctos
[- Agriotherium of recent authors], these two gen-
era forming a separate branch of the ursine stem.
14
DAVIS: THE GIANT PANDA
15
Ailurus, on the other hand, he considered a pro-
cyonid. Winge's views have been adhered to with-
out exception by continental European authors.
1901. Both Lankester and Lydekker, after in-
. / dependently studying the skull and limb bones,
concluded that Aeluropus and Aeliirus are closely
allied, that they are procyonids, and that the Pro-
cyonidae should be subdivided into two subfam-
ilies, the Procyoninae and the Ailurinae. ' This,
of course, is merely a re-affirmation of the earlier
views of Mivart. They emphasized the procyno-
nid-like presence of both protocone and hypocone
on the lingual border of P^ (the protocone is absent
in the Ursidae), the presence of an entepicondylar
foramen, and numerous "minute coincidences" in
the structure of the skull and long bones of the
limbs.
Lankester and Lydekker deemed it desirable
that Aeluropus, which hitherto had been called the
"parti-coloured bear," should henceforth be called
the "great panda." This appears to be the first
published reference to Ailuropoda as a panda.'
1902. Beddard, in his Mammalia, followed
Flower and Lydekker in placing "Aeluropus" in
the Ursidae and "Aelurus" in the Procyonidae.
1904. Weber, in the first edition of Die Sduge-
tiere, followed Winge in considering Aeluropus as
an ursid closely related to Hyaenarctos and refer-
ring Ailurus to the Procyonidae.
1913. Bardenfleth made a detailed study of
the dental and osteological characters of Ailuro-
poda and concluded that its resemblances to Ailu-
rus are due to convergent development of the
molar teeth based on herbivorous diet, and that its
closest affinities are with the extinct ursids of the
Hyaenarctos group.
1915. Woodward described the well-preserved
skull of a Pleistocene giant panda, which he named
Aelureidopus baconi, from Burma. This was the
first proof that the giant panda once had a more
extensive range than it has at present.
1921. Pocock, in a review of the classification
of the Procyonidae, concluded that both Ailuro-
poda and Ailurus represent distinct and separate
families. This view he re-affirmed in 1929 and also
in his article "Carnivores" in the fourteenth edi-
tion of the Encyclopaedia Britannica, where no
fewer than 13 families (compared with 7 of other
authors) and 29 subfamilies (18 of other authors)
of living fissiped carnivores are recognized. Po-
cock's "families" correspond roughly to the gen-
era of other authors.
' The word "panda," which had been applied to the lesser
panda (Ailurus) since the time of Cuvier, is "said to be a
Nepal name." (Oxford Universal English Dictionary.)
1923. Matthew and Granger described giant
panda material, under the name Aeluropus fove-
alis, from Pliocene deposits in eastern Szechwan,
thus farther extending the former range of the
giant panda.
1928. Weber, in the second edition of Die Sdu-
getiere, retained his views of 1904 as to the ursid
affinities of Ailuropoda.
1929. Theodore and Kermit Roosevelt shot a
giant panda at Yehli, Sikang Province. This in-
dividual, said to be the first giant panda shot by
a white man, was mounted, together with a sec-
ond skin purchased from natives, in a habitat
group in Chicago Natural History Museum. The
ensuing publicity started a cycle of "giant panda
expeditions" that have gi'eatly increased our knowl-
edge of the distribution, habits, and morphology
of this animal.
1936. Gregory examined the skull and denti-
tion of Ailuropoda, Ailurus, and various fossil and
recent procyonid and ursid carnivores. He con-
cluded that Lankester and Lydekker were correct
in referring Ailuropoda and Ailurus to the Procy-
onidae.
Raven, in the same year, studied the viscera of
a giant panda, which had been preserved in the
field by an American Museum expedition. He
listed six points of agreement between Ailuropoda
and Ailurus, and concluded that resemblances be-
tween the former and the bears "are an expression
of convergence in size and food habits."
1937. Mrs. Ruth Harkness, of New York City,
succeeded in bringing a living baby giant panda to
the United States. This individual, named Su Lin,
lived for 16 months in the Chicago Zoological Park.
It formed the basis for the present monograph.
The fanfare that surrounded the life and death
of Su Lin started a new series of expeditions for
living pandas. At least a dozen have since been
exhibited in the United States and Europe.
1943. Segall made a study of the auditory re-
gion in the arctoid carnivores. The structure of
the bony auditory region and auditory ossicles led
him to associate the Ailuridae (Ailurus and Ailuro-
poda) with the Ursidae.
1945. Simpson, in his Classification of Mam-
mals, adhered to the classical view of Mivart in
grouping Ailurus and Ailuropoda in the subfamily
Ailurinae of the family Procyonidae.
1946. Mettler and Goss, after studying the
topography of the brain of an adult giant panda,
concluded that "the configuration of the brain of
Ailuropoda melanoleuca is identical with that of
the bear."
1956. Leone and Wiens reported that compari-
sons of serum proteins by means of precipitin tests
16
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
V.
"clearly indicate that the giant panda belongs in
the family Ursidae."
An examination of this history of research is
instructive. There can be no doubt that the giant
panda occupies a more or less isolated position
among living carnivores, and that the features usu-
ally relied upon by mammalogists for determining
affinities are masked by si>ecializing adaptations
in this form. Two conclusions may be drawn from
these historical data.
1. Quite different conclusions have been
reached by a succession of capable investigators
on the basis of the same data. This indicates that
the data employed are not sufficient to form a basis
for an objective conclusion, and that opinion has
been an important ingredient in arriving at con-
clusions.
2. Opinion as to the affinities of Ailuropoda is
divided almost perfectly along geographic lines,
which shows that authoritarianism i-ather than ob-
jective analysis has really been the determining
factor in deciding the question. After the pioneer-
ing work of Milne-Edwards and Gervais, the first
attempt at determining the affinities of Ailuropoda
was made by Mivart in England. Mivart's con-
clusion that both the giant and the lesser panda
are procyonids has been echoed by every British
and American author down to 1943, except for the
short-lived dissenting opinion of Flower and Ly-
dekker.' In the meantime, on the continent,
Winge in 1895 relegated Ailuropoda to the Ursi-
dae and Ailurus to the Procyonidae, and every
subsequent continental authority has followed in
his footsteps. Such a cleavage of opinion along
geogi^aphical and linguistic lines cannot be due to
chance.
It is apparent that the relationships of Ailuro-
poda will never be decided on the basis of the data
afforded by the skeleton and dentition. Thus the
fii-st task of this study was to examine data not
previously available, with a view to determining
the much-discussed affinities of this carnivore.
> Beddard (1902) merely copied Flower and Lydekker.
DISTRIBUTION
The giant panda apparently has a very re-
stricted distribution in the high mountains of
western Szechwan and eastern Sikang in western
China. This is the area of the extremely complex
mountain escarpment that sharply separates the
Min River Valley from the Tibetan highland to
the west.
Localities where or near which specimens have
been collected are shown on the accompanying
map (fig. 1). The localities given on many mu-
seum specimens obviously represent the city where
the skin was purchased (e.g., Mouping, Ya-chou)
rather than the locality from which the specimen
actually came. Localities given in the literature
("Moupin," David, 1869; "mountains of Mou-
ping," Gervais, 1875; "Wassu mountains," "moun-
tains east of Min valley," Jacobi, 1923a) are often
very indefinite. Thus the localities that can be
plotted with any certainty on a map are relatively
few, although none of the unplottable localities ex-
tends the known range of this species. The dis-
tance between the southernmost record (Yehli)
and the northernmost (25 miles west of Wen-
chuan) is only about 175 miles. All records, ex-
cept Yehli are on the slopes of the Chuing-lai
mountains surrounding the valley of the Min
River. Yehli, where the Roosevelt brothers shot
their panda, is on the slopes of the Ta-liang Moun-
tains south of the Tung River.
Pen (1943) reported Ailuropoda horn "the up-
per source of the Yellow [Yangtze] River where it
connects the two lakes, the Tsaring Nor and the
Oring Nor, near the central part of Chinghai prov-
ince" at 34 7' N. Lat. Pen refers, without cita-
tion, to a record by Berozovski at 34 N. Lat., but
I have been unable to find such a reference. Pen
collected no specimens, but there seems to be no
reason for doubting his identification of the ani-
mals he saw. Even allowing this provisional ex-
tension of range, the north-south distribution
amounts to only about 470 miles.
Sowerby (1932) has suggested even greater ex-
tensions of the range of Ailuropoda. He writes:
"The range of the giant panda is now admitted to
be much more extensive than formerly supposed.
. . . We came across indisputable evidence of the
giant panda in the Tai-pei Shan region of South-
western Shensi, where the local takin hunters de-
scribed its appearance to us accurately and also
showed us its droppings and the places where it
had torn up the culms of bamboos for food. From
this region it ranges southward throughout all the
wilder mountainous areas at least to the Yunnan
border, eveiywhere being known to the native
hunters by its native name, pei-hsiung." Sowerby
(1937a) later defined the range as "more or less
restricted localities from the Tsing Ling range of
mountains in southern Shensi and eastern Tibet
to northern Yunnan." Others have emphasized
the unreliability of reports by native hunters, how-
ever, even after being shown pictures of the ani-
mal, and it seems best to await more positive
evidence before accepting Sowerby's broad exten-
sions of range.
Ailuropoda had a much more extensive distri-
bution in comparatively recent geological times,
as is shown by the two fossil records. Smith-
Woodward (1915) described a Pleistocene panda
under the name Aelureidopus baconi, from Mogok,
Northern Shan States, Burma. This is in the Irra-
waddy River drainage and is more than 500 miles
southwest of the southern limit of the panda's
range as now known. Granger (in Matthew and
Granger, 1923) found giant panda material, which
was named Aeluropus fovealis, in Pliocene deposits
near Wan-hsien in eastern Szechwan. Wan-hsien
is situated on the Yangtze River (of which the
Min is a tributary), about 250 miles due east of
Chengtu.
Vertical Distribution
The vertical distribution of Ailuropoda is as
limited as its geographic distribution. All who
have studied its habits agree that this animal is
sharply limited to the bamboo zone, which lies
between about 5,000 and 10,000 feet.
Limited to the Si-fan region at altitudes of 1600 to 3300 m.,
consequently to the region of almost impenetrable bamboo
jungle on the steep slopes. Here it forces tunnels through
the thickets, which are IJ-^ to 5 m. high and are often
matted by snow pressure. (Jacobi, 1923b, p. 72.)
... in the bamboo jungles in altitudes varying between
six and fourteen thousand feet. We came to the conclusion
that it could safely be assumed that where there were no
17
Fig. 1. Western Szechwan and eastern Sikang provinces, showing locality records for Ailuropoda melanoleuca.
18
DAVIS: THE GIANT PANDA
19
bamboo jungles, there were no beishung. (Theodore and
Kermit Roosevelt, 1929, p. 261.)
The limits of the giant panda's altitudinal range is deter-
mined largely by the extent of the bamboo growth. Two
exceptions to this statement were observed, however. In
one case we found unmistakable panda droppings high on
the Chen Lliang Shan range, 1000 feet above the rhododen-
dron forest, and probably 1500 feet above the nearest bam-
boo. It was interesting to find that on occasion the panda
must travel above its regular habitat to the bare grasslands
of the blue sheep country. In another instance I saw where
a giant panda had climbed a small pine tree just above the
village of Tsapei on Chengou River. It was located 300 feet
above the river bottom on an open slope, with the nearest
bamboo across the valley. (Sheldon, 1937.)
The vertical distribution of the bamboo bear, which avoids
the hot arid canyons as well as the high alpine zones, extends
on the high levels between 1500 and about 4000 m., where it
is closely confined to the moist, subtropical bamboo zone.
(Schiifer, 1938.)
Pen's sight record of a giant panda at the upper
source of the Yangtze River was on the open steppe
of the Tibetan plateau. He speculates that these
animals may have reached the plateau country by
migrating north and west along the bamboo zone
of the mountains, and that there is here an annual
summer migration onto the plateau, with a winter
retreat into the less rigorous environment of the
mountains.
HABITS AND BEHAVIOR
Because of the inaccessible and rugged nature
of its habitat, there has been httle field observation
of the giant panda. Various authors have re-
corded information, beginning with the original
notes of David, and the observations are in close
agreement. Details of behavior are known only
from observations on captive individuals (Schnei-
der, 1939; Haas, 1963).
HABITAT
The giant panda appears to be closely confined
to the moist bamboo zone on the slope of the high
mountains. The bamboo culms, which are slender
(up to an inch and a half in diameter) and grow
to a height of 10 to 12 feet, form dense impene-
trable thickets that are often matted by snow pres-
sure. The bamboo jungle is associated with forests
of fir trees, and at higher altitudes the bamboo
gives way to rhododendron, into which the panda
does not wander. The mountain slopes "under
the influence of the summer-like monsoon rains,
exhibit a comparatively mild subtropical climate."
(Schafer, 1938.)
The panda shares this habitat with such other
large mammals as the golden monkey (Rhinopithe-
cus), leopard (Panthera pardus), red dog {Cuon al-
pinus), black bear (Ursus thibetanus), wild pig
(Sus cristatus), barking deer (Muntiacus), serow
(Capricornis), and takin {Budorcas). Only the
leopard and the red dog would be likely to attack
the giant panda, and such encounters would be
uncommon.' Thus the giant panda is practically
without natural enemies an important point in
estimating the selection pressures to which this
species is subjected.
Wilson (1913) described the vegetation on the
mountain Wa Shan as follows:
At one time a dense forest of Silver Fir covered the moun-
tain. . . . Some of these Firs could not have been less than
150 feet in height and 20 feet in girth. . . . Besides the Silver
Fir (Abies Delayayi), the only other conifers are Tsuga yun-
nanensis, Juniperus formosana, and Picea complanata. Rho-
dodendrons constitute the conspicuous feature of the vege-
' Seton (Lives of game animals, 2, 1929) lists the grizzly
bear and the mountain lion as enemies of the American black
bear, an animal about the same size as the giant panda.
tation. . . . They begin at 7500 feet, but are most abundant
at 10,000 feet and upwards. In the ascent I collected 16
species. They vary from diminutive plants 4 to 6 inches
high, to giants 30 feet or more tall. . . . One of the common-
est species is R. yanthinum. . . . Above this [7200 feet], for
500 feet, comes a wellnigh impenetrable thicket of Bamboo
scrub. The species (Arundiruiria nilida) is of remarkably
dense growth, with thin culms, averaging 6 feet in height.
Next above this, till the plateau is reached, is a belt of mixed
shrubs and herbs, conspicuous amongst which are Syringa
Sargentiana, Hydrangea anomala, H. villosa, Neillia affinis,
Dipelta ventricosa, Ribes longeracemosum, var. Davidii, Enki-
anthus deflexus, Styrax roseus, Deutzia (2 spp.), Rubus (5 spp.),
Viburnum (4 spp.), Spirea (4 spp.), Acer spp., Malus spp.,
Sorbus spp., Meconopsis chelidonifolia, Fragaria filipendulus,
Lilium giganteum, and the herbs of the lower belt. A few
Rhododendrons occur chiefly on the cliffs. The plateau
(8500 feet) is about half a mile across, marshy in places,
and densely clad with shrubby vegetation and Bamboo
scrub. . . . From 10,000 feet to the summit of the mountain
Rhododendron accounts for fully 99 per cent of the ligneous
vegetation.
FOOD
All observers (except Pen, see below) agree that
in its native state the giant panda subsists exclu-
sively on bamboo. McClure (1943) identified the
bamboo native to the haunts of the giant panda
as Sinariindinaria sp.
"Its food seems to consist exclusively of bamboo shoots,
but by no means merely the young shoots, which even man
himself eats with relish, but also those as thick as a finger.
In winter, in fact, only strongly woody and silicified stalks
are available. All this can be ascertained from fresh drop-
pings, which consist almost exclusively of chewed-up stalks,
often as long as a finger joint, whether in the middle of July
or in the beginning of January." (Jacobi, 1923a.)
Not only is the giant panda entirely herbivorous, but it
is known to live on the dwarf bamboo of the northeastern
spur of the Himalayas to the exclusion of all other vegetable
matter. . . . The food supply in the mountains of west
Szechuan is inexhaustible. . . . We found giant panda eating
not only the bamboo shoots, but the stalks and leaves of
fully mature sprouts, often an inch and one-half in diam-
eter." The author followed a fresh morning trail and found
"that at an average of every hundred yards there were from
one to three large droppings (4 to 6 inches long and 2 inches
thick, tapering at each end). At a conservative estimate
there were 40 droppings. . . . Below the resting place was a
pile of at least 30 more droppings, making a total of 70 ex-
creted between early morning and 9 a.m These droppings
20
DAVIS: THE GIANT PANDA
21
Fig. 2. Sitting posture and use of fore paws in Ailuropoda. A-C, "Happy" eating bamboo in Leipzig Zoo (from Schneider,
1939). D, Mei Lan eating green cornstalks in Chicago Zoological Park.
emerge almost totally undigested. It seems logical to assume
that an animal of such large proportions must have to eat
tremendous quantities to secure the nourishment that it
requires. ... I estimate that they would have to spend
from 10 to 12 hours a day feeding. (Sheldon, 1937.)
The bear [Ailuropoda] prefers the young and succulent
bamboo shoots to the woody stems. For this reason, in the
main district of bamboo-bears I found no bamboo shoots in
the spring, since they had been systematically 'browsed' by
bears. The bulk of its nourishment consists, however, of
stone-hard bamboo stems thicker than a finger. With
its powerful molar teeth the bear bites off the 3 to 6 m.
long stems about 20 to 40 cm. above the ground, lays them
down and eats the middle part up to the beginning of the
leaves, while it regularly rejects the lower, hard part and
lets it lie. Such chewed places are not particularly hard to
find, although they are always concealed in the middle of
the jungle. Usually they are not larger than one to two
square meters. In these places perhaps 15 to 20 stems are
bitten off, and the rejected parts cover the ground. (Schafer,
1938.)
McClure (1943) listed nine species of bamboo
that are palatable to the giant panda, expressing
astonishment at the range of its tastes. Sowerby
(1937a) stated that a half-grown pet giant panda
that wandered at will on a Chinese farmer's land
"ate grass and other plants."
Pen (1943) stated that a giant panda he ob-
served at a distance of 2000-3000 meters on the
22
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Fig. 3. Use of fore paws in pandas. A, Ailuropoda (Mei Lan) using both fore paws to manipulate food; Chicago Zoological
Park, September, 1952. B-D, Lesser panda (Ailurus fulgens) using fore paws to manipulate bamboo; Lincoln Park Zoo.
Tibetan plateau was eating plants of various kinds,
"principally gentians, irises, crocus, Lycium chi-
nense and tufted grasses." Unfortunately it is not
clear from his description how careful his observa-
tion was, and this is the only reported field obser-
vation of the giant panda's eating anything other
than bamboo.
Captive specimens of Ailuropoda have eaten
in addition to various bamboos porridge, green
corn stalks and ears, stalks of celery, carrots, and
other vegetables. They refuse meat in captivity.
Thus in nature the giant panda lives immersed
in its food supply. It has practically no natural
enemies, does not pursue prey, and does not need
to wander in search of food. Demands on loco-
motor efficiency are absolutely minimal.
FEEDING AND MANIPULATION
OF FOOD
The manner of eating bamboo was well described
by Schneider (1939), who carefully observed a
200-pound female temporarily exhibited in the
Leipzig Zoo. The animal always sat or lay when
eating bamboo, thus freeing the fore feet (fig. 2).
Only the stalks were eaten; the leaves were re-
jected. The bamboo stalks were held in the fore
foot and carried to the mouth. The tough outer
layer was quickly and skillfully stripped off with
DAVIS: THE GIANT PANDA
23
the incisors, in which case the stalk was inserted
transversely into the mouth, or with the canines
and anterior premolars, in which case it was shoved
lengthwise between the upper and lower tooth-
rows. The stripped outer layer was torn off with
a twisting movement of the fore foot coupled with
a lateral turning of the head. The peeled stalk
was then placed crosswise in a corner of the mouth,
at the level of the large cheek teeth, where it was
bitten off and chewed up.
The giant pandas in the Chicago Zoological Park
manipulated green corn stalks, celery stalks, and
carrots in a similar manner. The animals invari-
ably sat down, or stood on their hind legs with
one fore leg braced against the bars of the cage,
when eating such food. They often sat with a
piece of corn stalk or a carrot in each fore paw.
Items were carried to the mouth in the fore paw,
inserted transversely between the large cheek teeth,
and bitten off. Chewing was a succession of ver-
tical chopping movements.
Field observers (Weigold in Jacobi, 1923a; Shel-
don, 1937) have emphasized the poorly chewed
and undigested condition of pieces of bamboo in
the droppings of the giant panda.
The skill and precision with which objects are
grasped and manipulated by the fore feet is aston-
ishing. I have observed animals in the Chicago
Zoological Park pick up small items like single
straws and handle them with the greatest pre-
cision. Small disks of candy less than an inch in
diameter were handled deftly and placed in the
mouth. Objects are grasped between the radial
pad and the palmar pad and are held in the shal-
low furrow that separates these two pads. The
actions of the fore paw suggest a human hand
grasping through a thumbless mitten but are less
clumsy than this comparison would indicate.
Bears and raccoons, of course, can grasp objects
with their fore paws. In this action the digits,
aligned side by side, are closed over the object,
which is thus held between the digital pads and
the transverse palmar pad. This is a quite differ-
ent mechanism from the grasp of the giant panda.
The lesser panda (Ailurus) grasps objects almost
as skillfully as the giant panda, and apparently in
a similar way (fig. 3).
Diets of Other Carnivores
It is remarkable that the food habits of none
of the bears have ever been adequately studied.
Cottam, Nelson, and Clarke (1939) analyzed the
contents of 14 stomachs of black bears (Ursus
americanus) killed in early winter, and found that
fruits and berries, mast, and foliage accounted
for 93 per cent of the bulk and vertebrates for 4
per cent. Brehm (1915, Tierleben, Saugetiere, 3,
p. 394) states that "more than the rest of the
carnivores, the bears appear to be omnivorous in
the fullest sense of the word, to be able to nourish
themselves for a long time from the plant king-
dom alone." Seton (Lives of Game Animals, 2,
(1), 1929) emphasizes the omnivorous nature of
the diet of each of the species of North Amer-
ican bears.
No quantitative study of the diet of Bassariscus
has been made. Grinnell, Dixon, and Linsdale
(Fur-bearing Mammals of California, 1, p. 179)
state that "mice and other small rodents consti-
tute the largest part of the food eaten by the ring-
tailed cat. Small birds and berries are the other
two most important items found in the stomachs
examined. . . . Their jaws and teeth were so strong
that they could chew up the leg bones of chicken
without any trouble."
The seasonal or annual diets of several other
American arctoid carnivores have been determined
quantitatively through large-scale analysis of stom-
ach contents and scats. These, of course, provide
the only reliable data on the diet, as opposed to
what may be eaten under exceptional circum-
stances, of any animal that is not positively re-
stricted to a single food item. The diet of Procyon
is more than 50 per cent (by bulk) vegetable (fruits,
berries, nuts, and grains). Among the Canidae,
the fall and winter diet of the red fox (Vulpes) is
about 20 per cent herbivorous (fruits, grains,
grasses), the winter diet of the gray fox (Urocyon)
about 20 per cent herbivorous, and the annual diet
of the coyote (Canis latrans) only 2 per cent her-
bivorous. Many mustelids (Mustela vison, Taxi-
dea, Lutra) are exclusively carnivorous or nearly
so, but the skunks {Mephitis, Spilogale) may in-
clude up to 50 per cent of plant material in their
diets.
From these data it is evident that the closest
living relatives of the giant panda (the Ursidae)
are, next to Ailuropoda itself, the most herbiv-
orous of living carnivores.' If the diet of Procyon
is typical, the Procyonidae are likewise heavily
herbivorous, though less so than the bears. The
dogs and foxes are true carnivores, including only
relatively small amounts of plant material in their
diets. Thus Ailuropoda is a member of a group
of carnivores (the procyonid-bear branch) that is
already heavily herbivorous, and it is most closely
related to the most herbivorous element of this
group. The exclusively herbivorous diet of the
' Unfortunately, no information, beyond vague general
statements, is available on the diet of the lesser panda
(Ailurus). Sowerby (1936a) says it feeds largely on bamboo
leaves, and specimens in the Lincoln Park Zoo in Chicago
ate green bamboo ravenously.
24
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Fig. 4. Postures of Ailuropoda: standing (Mei Lan, Chicago Zoological Park) and climbing ("Happy," Leipzig Zoo).
giant panda is merely an extension, via an inter-
mediate stage (the Ursidae), of a non-carnivorous
dietary trend already present in the group from
which this species was derived.
POSTURE
The postures of Ailuropoda are similar to, but
by no means identical with, the corresponding pos-
tures of Ursus.
The normal standing posture is similar to that of
bears. Both fore and hind feet are fully planti-
grade but are toed in more sharply than in Ursus.
The prominent shoulder hump of bears is much
less conspicuous in Ailuropoda, and the hind quar-
ters are somewhat higher. As in bears, there is
relatively little angulation at elbow and knee. The
head is carried low, and the tail is clamped tightly
against the body. The panda has a stocky appear-
ance, less dog-like than that of bears.
The animal often sits on the hind quartei's with
the fore feet free of the ground. This posture is
almost invariably assumed during eating, since it
frees the fore feet for manipulating food (fig. 2).
The panda does not normally sit erect, as bears
often do, with the weight resting on the ischial
surfaces. Instead, the back is curved like the let-
ter C, and the weight appears to rest on the pos-
terodorsal surface of the pelvis. In this posture
the hind legs are thrust forward, their lateral sur-
faces resting on the ground, with the knees slightly
bent and the soles of the hind feet turned inward.
Bears sometimes sit with their hind legs similarly
extended, although more frequently the legs are
drawn up in dog fashion.
Ailuropoda often rests, half sitting and half re-
clining, in the crotch of a tree. The back is then
arched sharply, the weight resting on the lower
part of the back rather than on the ischia.
Like bears, Ailuropoda readily stands erect on
its hind legs (fig. 4). This posture is assumed both
in the open without any support for the fore feet
and, more frequently, with the fore feet resting
against the bars of the cage. The hind feet are
nearly fully plantigrade, the femur and tibia in a
straight vertical line. The zoo animals show no
DAVIS: THE GIANT PANDA
25
17
Ursus
AUuropoda
Fig. 5. The eight phases of the slow diagonal walk, with its footfall formula, of AUuropoda and Ursus americanus.
Tracings from motion picture film taken at 16 f.p.s. Numerals are frame numbers in the sequences.
more tendency to stand erect than bears do. I
have never observed a panda walking in the erect
position. "Bears are able to stand erect on their
hind legs, and to walk a short distance in an un-
steady but not particularly awkward movement."
(Brehm.)
LOCOMOTION
The normal gait of the giant panda is a "fast
diagonal walk" (figs. 5, 6) in A. B. Howell's termi-
nology. Howell (1944) states that this gait is reg-
ularly employed by nearly all mammals. It is
used by bears and raccoons. When moving more
rapidly the panda breaks into a clumsy trot.
Whether it is capable of galloping at still higher
speeds is not known.
The walk of AUuropoda is bear-like, but less
smooth and graceful. The head is carried well
below the shoulder line, and the tail is closely ap-
pressed against the body. The stride is consider-
ably longer than in bears, and as a result the gait
is more rolling, with much more lateral rotation of
the shoulders and hips than in Ursus. This gives
a pronounced waddling character to the locomo-
tion. The heavy head is swayed from side to side.
The sole of the fore foot is fully apposed to the
ground, but the heel of the hind foot does not
touch the ground. Indeed, the panda appears to
be incapable of flexing the ankle joint enough to
permit plantigrady (p. 144). In this respect AUu-
ropoda contrasts with Ursus, in which the sole is
naked to the heel and the foot is fully plantigrade.
During the recovery phase of the stride the fore
feet are directed inward much more than in Ursus,
and this "pigeon-toed" position of the foot is main-
tained during the support phase. During the re-
covery phase the hind feet are rotated medially so
that the soles are directed medially. During the
support phase, when the hind foot is resting on
the ground, the toes point inward. At the end of
the support phase the feet roll off the ground with
the lateral toes receiving the major thrust.
26
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Fig. 6. Two types of walking loco-
motion in the giant panda Mei Mei. The
top figure is the fast diagonal walk, cor-
responding approximately to no. 19 in
figure 5. The bottom figure is a slow
walk.
In captivity the giant panda is a persistent
climber when young (fig. 4). The movements are
often astonishingly clumsy but successful. In
climbing vertical or near vertical tree trunks the
movements are bear-like. The animal embraces
the tree, with the soles of all four feet pressed
against the bark, and progresses by a series of
"caterpillar" movements. The animal takes ad-
vantage of branches or other projections to hoist
itself up. It descends tail first, unless the slope is
gentle enough to allow it to walk down head first.
The claws appear to be of less importance in
climbing than the friction of the soles against the
bark, although the claws are used, especially if the
animal slips unexpectedly. In this type of climb-
ing, called "bracing" or "prop" climbing {Stemm-
klettern) by Boker (1935), the portion of the body
not supported by the hind legs is suspended from
the fore legs.
DISPOSITION
Young individuals are active and playful, and
thousands of zoo visitors have been entertained
by their clownish antics. As they grow older they
become much less active. Some individuals, at
least, become siu'ly and dangerous in captivity. The
giant panda "Mei-Lan," while in captivity in the
Chicago Zoological Park, mauled one of his keepers
so severely that an arm had to be amputated.
Sheldon (1937), who hunted Atluropoda, wrote:
"My experience convinced me that the panda is
an extremely stupid beast. On one occasion at a
distance of 350 yards I obsei-ved two individuals
on the edge of a bamboo jungle. Driven out by
four dogs and warned by several high-powered
bullets whistling about them, neither animal even
broke into a run. The gait was a determined and
leisurely walk. Again, Dean Sage and I observed
another panda pursued by four dogs. In this in-
stance he walked to within eight feet of Dean and
was stopped only by bullets. He gave absolutely
no evidence that he saw either of us, and seemed
completely to disregard both the shots and the
loud talking and shouts of a few minutes previous."
SUMMARY
The giant panda is confined to the moist bam-
boo zone on high mountain slopes, where the leop-
DAVIS: THE GIANT PANDA
27
ard and the red wolf are its only potential natural
enemies. Its natural diet consists exclusively of
bamboo, with which it is always surrounded. Se-
lection pressure for locomotor efficiency is abso-
lutely minimal. Bamboo stalks are consumed in
enormous quantities, but are poorly chewed and
poorly digested. The fore feet are constantly used
to manipulate the food. Objects grasped in the
fore paws are held between the radial pad and the
palmar pad. This grasping mechanism differs
from that used by bears and raccoons but is sim-
ilar to that of the lesser panda {Ailurus).
Ailuropoda is a member of a group (the bear-
raccoon line) of carnivores whose diet is more than
50 per cent herbivorous. Its closest living rela-
tives (the bears) appear to be more than 90 per
cent herbivorous.
Posture and locomotion are similar to those of
bears. Locomotion is less efficient. Ailuropoda
climbs clumsily but persistently when young.
EXTERNAL CHARACTERS
The general habitus of Ailuropoda is ursine.
The head and fore quarters are heavy and power-
ful, the hind quarters relatively weak. The build
is much stockier than that of bears of comparable
size.
I. DESCRIPTION
The pelage is thick and woolly, as befits an ani-
mal frequenting high altitudes. The characteristic
parti-colored pattern is shown in figui-e 9. This
pattern is unique among carnivores, although it is
approached by the ratels {Mellivora}, and by the
lesser panda (AiluriLs) except that the areas that
are white in Ailuropoda are for the most part red-
dish-brown in Ailurus. The coloration of Ailuro-
poda is certainly a "constitutional" pattern rather
than a "biological" pattern conditioned by nat-
ural selection.
The most unusual feature of the hair arrange-
ment is found in the nasal region. The short hair
on the top of the rostrum, from a point just in front
of the eyes down to the muzzle (a distance of about
55 mm.), is directed straight forward. Two whorls
are formed, 35 mm. apart, in front and mesad of
the eyes, from which the hair radiates. Attention
was first drawn to this character, which is unique
among arctoid carnivores, by Kidd (1904). Kidd's
later suggestion (1920), that this reversal of hair
stream resulted from rubbing the hair toward the
muzzle in cleaning it, cannot be taken seriously.
It is noteworthy that a similar reversal occurs in
other short-nosed carnivores (e.g.,Fefe).
The facial vibrissae (fig. 7) are rather feebly de-
veloped, although not so poorly as Pocock (1929)
concluded from an examination of prepared skins.
The superciliary tuft is represented by about three
moderately long hairs over the eye. There is a
relatively heavy growth of mystacial bristles along
the upper lip, extending back almost to the angle
of the mouth. On the lower lip they extend as far
as the angle of the mouth. These bristles are much
worn and broken on the specimen at hand, so that
their length cannot be determined. They cer-
tainly do not reach any great length, however.
Inter-ramal and genal tufts are absent.
The rhinarium, as pointed out by Pocock, is
hairy above, with a well-haired infranarial area on
either side of the midline below. The naked area
roughly resembles an inverted triangle and is con-
tinued ventrally into a short, grooved philtrum.
There is also a V-shaped notch between the nos-
trils dorsally. The transverse groove below the
nostrils referred to by Pocock is not evident on the
fresh animal. The nostrils are transverse.
The external ear is erect, relatively larger than
in bears, arising from a curiously constricted base.
The margin is rounded, as in bears. The ear is
well haired internally far down into the meatus.
There is no bursa. The height of the pinna in
Su Lin is about 85 mm., its breadth about 80 mm.
The eai-s are set higher on the head and closer to-
gether than in bears a consequence of the enor-
mously developed masticatory musculature.
The fore foot (fig. 8) is short and powerful. The
digits are enclosed in the common skin of the foot
up to the base of the digital pads. Examination
of the fresh animal corrects several errors made by
Pocock. All the pads are thick and cornified. The
digital pads are elUptical in outline, those of the
second, third, and fourth toes approximately equal
in size. That of the fifth toe is slightly smaller,
and the pad of the poUex is the smallest of all and
is joined to the palmar pad by a narrow isthmus
of naked skin. The palmar pad extends as a nar-
row strip across the entire foot. There is no evi-
dence of its breaking up into interdigital pads.
The outer end of the pad is expanded slightly,
and its inner end curves proximally to join the
prominent radial lobe, from which it is separated
by a transverse furrow.
The radial lobe is smaller than the outer carpal
lobe. This lobe is wanting in bears. It is ellip-
tical in outline, the long axis running anteroposte-
riorly, and is hemispherical in cross section. It is
associated with the prominent radial sesamoid
bone, which hes directly beneath it; Pocock was
not sure that it represents the missing inner carpal
lobe. Objects held in the hand lie in the furrow
between the radial lobe and the inner end of the
palmar pad and are grasped between these two
pads.
The outer carpal lobe is large and roughly cir-
cular in outline and is situated somewhat farther
28
Fig. 7. Side view of head of Ailuropoda, showing pattern of vibrissae and hair-slope.
29
Fig. 8. Ventral surfaces of left fore and hind feet of Ailuropoda melanoleuca (A, B) and Ursus americanus (C, D). Ursus
after Pocock reversed.
30
DAVIS: THE GIANT PANDA
31
proximally than the radial lobe, lying about a third
of its own width behind the palmar pad, much
closer than in Ursus.
The remainder of the palmar surface is densely
covered with long hair.
The hind foot (fig. 8) is slightly narrower than
the fore foot and is remarkable for the limited ex-
tent of the cornified hairless areas. The absence
of the posterior lobe of the plantar pad is associ-
ated with the inability of Ailuropoda to flex the
foot beyond 45 from the vertical (fig. 80). The
digits are enclosed in the common skin of the foot
nearly to the bases of the digital pads. The digital
pads are elliptical in outline, and all are approxi-
mately the same size. The pad of the hallux is
joined to the plantar pad by a narrow isthmus of
naked skin similar to that on the pollex. The
plantar pad is a narrow transverse cushion, feebly
convex anteriorly and very faintly divided into
five lobes (not four as Pocock stated). The pad
lies beneath the metatarso-phalangeal articulation.
It is somewhat wider at the outer end than at the
inner, and the lobe under the hallux is more clearly
indicated than the others are. Metatarsal pads
are absent; the remainder of the sole is densely
covered with long woolly hair.
The claws on all the digits are strongly com-
pressed and taper from a wide base to a sharp tip.
The upper edge of the claw describes almost a per-
fect quadrant of a circle; the lower edge is sinuous.
The tail is relatively small but longer and con-
siderably heavier than that of any of the bears.
It measures 115 mm. in length in Su Lin (the cau-
dal vertebrae measure 203 mm. in the skeleton of
an adult) and tapers abruptly from a heavy base.
The base of the tail is flattened dorsoventrally; its
width is about 35 mm. while its depth is only about
25 mm. (see p. 83). The entire organ is densely
clothed in long, coarse hairs.
There are two pairs of nipples, one pair pectoral
and the other abdominal. The pectoral pair lies
over the seventh rib, the abdominal pair 200 mm.
behind the posterior end of the sternum. The
bears have three pairs of mammae.
The external structures in the perineal region
are described on page 221.
II. MEASUREMENTS
No flesh measurements of an adult giant panda
are available. The following measurements were
made on the mounted skeleton of the adult male
killed by the Roosevelt brothers. Flesh measure-
ments of an adult female black bear, quoted from
Seton (1929, Lives of Game Animals, 2 (1), p. 119)
are given for comparison.
Ursus
Ailuropoda americanus
mm. inches mm. inches
Snout to tail tip 1422 56 1613 63.5
(along curve)
Tail 203 8.5 127 5
Height at shoulder. .. . 635 25 648 25.5
Approximate mean pounds pounds
weight of adult 275 250
The female "Happy" (weight 223 pounds), meas-
ured by Schneider (1939), had a shoulder height of
about 660 mm.
No actual weight figures for adult giant pandas
exist. Schafer estimated that an adult male would
weigh 275 pounds; Ailuropoda is fully grown at
4-5 years. The adult male Mei Mei weighed 205
pounds at death but weighed 296 pounds some
months earlier. The weight of the male Mei Lan
was estimated by zoo officials at 300 pounds when
he was six yeai's old. Skeletal measurements (Ta-
ble 6, p. 45) show that Mei Lan was much the
largest panda on record. A male at the St. Louis
Zoo weighed about 280 pounds at eight years of
age, and a female 240 pounds at five years. Thus
it appears that the adult weight of the giant panda
is 250-300 pounds, which is close to the average
for the American black bear. The giant panda
Su Lin weighed 132 pounds at death. The snout-
vent length of this individual was 1195 mm.
III. GROWTH
Weight increments for about the first 18 months
of life are available for three individuals. These
figures are, of course, for captive animals and do
not include the first month or two after birth.
Figures for "Pandah" and "Pandee" were kindly
supplied by Dr. Leonard J. Goss of the New York
Zoological Society. Weight figures are shown in
the accompanying graph (fig. 9). The average
monthly gain was 9 pounds.
IV. PROPORTIONS
Measurements of the linear dimensions of ana-
tomical structures serve two different purposes.
The simpler of these is as a means of expressing
relative sizes of homologous parts in two or more
organisms. Thus, if femur length is 75 mm. in A
and 60 mm. in B, we say that the femur is longer
in A, or is 15 mm. longer, or we may express the
difference as a percentage and say that femur
length in B is 80 per cent of femur length in A.
Such simple manipulations are much used in tax-
onomy and comparative anatomy. They rarely
present serious difficulties as long as the organisms
being compared are fairly closely related.
On the other hand, attempts to compare pro-
portions between two or more species or genera
32
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
often present serious difficulties. If A and B rep- they are not). This difficulty has plagued corn-
resent different species, the fact that the femur of parative anatomists from the beginning and has
A is longer than that of B may reflect the fact never been satisfactorily resolved.
7 8 9
MONTHS
Fig. 9. Growth curves of Ailuropoda.
that A is a larger organism than B, or that the
femur is relatively longer in A or is relatively
shorter in B, or a combination of all of these fac-
tors. The difficulty in determining what is in-
volved arises from the fact that there is no com-
mon standard to which the variable (in this case
femur length) can be related; for practical pur-
poses all measurements on an organism must be
treated as independent variables (although in fact
Many structures in mammals function as lever
systems. Interpretation of the mechanical advan-
tage of one lever system over another does not
depend on knowing how the differences in propor-
tions were achieved, but a true understanding of
the morphology of the organism obviously does.
Index figures, obtained by dividing one dimension
(e.g., tibia length) by another larger dimension from
the same individual (e.g., femur length) and multi-
DAVIS: THE GIANT PANDA
33
Fig. 10. Body outlines of representative arctoid carnivores to show posture and proportions. All drawn from photo-
graphs of living animals (not to scale). Top: Wolverine {Gulo luscus), a generalized mustelid; cacomistl (Bassariscus astutus),
a generalized procyonid. Middle: Raccoon (Procyon lolor) and les.ser panda (Ailurus fulgens). Bottom: Black bear {Ursus
americanus) and giant panda (Ailuropoia melanoleuca) .
plying by a constant (commonly 100), ai-e widely
used because they are independent of the absolute
size of the original figures and therefore directly
comparable between individuals of the most di.s-
parate sizes. Uncritical comparisons of such index
figures may, however, lead to grossly ei-roneous
conclusions. In the present study the femoro-
length tibia
tibial index
X 100
for a group of
length femur
badgers happened to be identical with the corre-
sponding index for a series of giant pandas, 76 in
both cases. Analysis of the figures for femur and
tibia length, using a third dimension (length of 3
vertebrae) as a common standard, revealed that
the tibia is abnormally short and the femur about
normal in the badgers, whereas in the panda the
reverse is true: the femur is abnormally long and
the tibia about normal. These relationships may
be of no importance in comparing the limbs as
lever systems, but they are of the utmost impor-
tance in interpreting the morphology, and partic-
ularly the phylogeny, of the limbs. They could
not have been detected from the dimensions of
femur and tibia alone, but required the use of a
third dimension as a common standard.
Body Proportions
Comparative proportions of the body in a series
of animals may be expressed by equating spine
length to 100 and expressing the dimensions of
other body parts as percentages of spine length
(Hildebrand, 1952). These proportions are shown
pictorially (fig. 10) and graphically (fig. 11) for a
series of carnivores.
34
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
23.5
76.5
Gulo luscus
Potos flovus
21.5
27
73
\
o
CO
CO
00
00
5
^
\
fO
to
o
00
00
CD
Ursus arclos
Ailuropoda melanoleuca
Fig. 11. Body proportions in representative carnivores (based on one specimen of each). In each case pre-sacral vertebral
length was equated to 100, and lengths of other parts were indicated as percentages of vertebral length. Limb length is the
"functional limb length" of Howell (lengths of propodium + epipodium + metapodium).
The wolverine {Gulo) represents a generalized
terrestrial carnivore, in which length of hind limbs
exceeds that of fore limbs by about 10 per cent,
the epipodial segments (radius and tibia) are
slightly shorter than the propodials (humerus and
femur), and the metapodials (metacarpals and meta-
tarsals) are long. In an arboreal carnivore (Potos)
the hind limbs are elongated and the metapodials
slightly shortened. In canids, which are typically
cursorial runners, the legs are relatively long, espe-
cially the epipodial and metapodial segments.
These all represent rather obvious adaptations
for locomotor efficiency. Adaptation is less obvi-
ous in certain other carnivores. The bears, which
are mediportal ambulatory walkers (p. 38), have
legs relatively as long as the cursorial canids and
the proportion between length of front and hind
limb is about normal for carnivores. The bears
and the giant panda are remarkable among carni-
vores in having a long femur associated with a
short tibia, without corresponding reduction in
radius length; this condition is characteristic of
heavy graviportal mammals (A. B. Howell, 1944).
In Ailuropoda the spine has been shortened by
elimination of lumbar vertebrae, a condition other-
wise unknown among carnivores. The trunk in
Ailuropoda is relatively shorter than in any other
known carnivore; the index "length thoracics 10-
12/length thoracolumbar vertebrae X 100" is 18
and 22 for two pandas, whereas it is 14 (13-15) for
all other carnivores examined except a specimen
of Mellivora, for which it is 16. This exaggerates
apparent leg length, but the legs actually are rela-
tively long (Table 2). Length of fore and hind
legs is subequal in Ailuropoda; this condition is
otherwise encountered among carnivores only in
the hyenas, although the proportions of the limb
segments in hyenas are quite different from those
of Ailuropoda.
Limb Proportions
In studies on small rodents, body length (meas-
ured on the freshly killed animal) is often used as
the independent variable. This is impractical in
work on skeletons of large mammals, for which
measurements of body length are rarely recorded.
Hildebrand (1952) used length of the vertebral
column in his work on body proportions of the
Canidae. Length of vertebrae probably varies as
little as any convenient linear dimension, but for
material as heterogeneous as the whole Order Car-
nivora it is desirable to eliminate the lumbar re-
gion, which, like the limbs, is intimately involved
in the mechanics of locomotion and would there-
DAVIS: THE GIANT PANDA
35
Table 1. LIMB SEGMENT RATIOS IN CARNIVORES
No.
Canis lupus 4
Canis lalrans 3
Chrysocyon brachyurus 2
Bassariscus astutus 4
Bassaricyon 3
Nasua 3
Procyon lolor 4
Potos flavus 3
Ailurus fulgens 3
Ursus americanus 2
Ursus arctos 2
Ailuropoda 7
Gulo luscus 3
Martes pennanti 2
Taxidea taxus 3
Mellivora 1
Lutra canadensis 3
Enhydra 2
Viverra tangalunga 5
Paradoxurus 4
Herpestes 1
Felis onca 2
Felis leo 4
Felis tigris 1
Total 71
humero-
Femoro-
Femoro-
Tibio-
Inter-
radial
humeral
tibial
radial
membral
index
index
index
index
index
100.6
89.8
98.4
90.7
98.5
104.4
87.8
99.6
92.0
89.9
108.1
91.0
107.8
91.4
91.2
79.0
89.8
97.2
72.8
81.4
74.8
88.5
101.7
65.4
76.9
85.1
82.4
91.0
76.9
79.8
100.9
85.3
100.8
83.6
83.5
80.6
89.2
94.9
74.9
84.2
74.7
94.9
94.2
75.3
85.5
81.1
86.4
72.2
96.9
90.8
81.5
84.2
68.5
100.2
90.6
77.1
98.4
76.1
98.5
99.3
78.9
94.3
90.2
82.5
88.8
76.0
90.4
99.0
69.4
79.9
76.2
98.2
76.1
98.1
98.1
79.9
90.2
75.5
95.5
92.5
71.5
98.9
111.4
63.5
80.2
75.7
95.9
112.4
64.6
79.7
90.1
81.3
96.2
76.1
78.8
77.0
91.7
90.9
77.5
84.9
76.5
82.9
90.3
70.3
76.9
77.6
87.0
80.9
85.4
86.0
90.3
86.5
84.6
92.3
89.2
81.3
83.6
82.2
82.7
83.2
fore be expected to bias the results. A group of
three thoracic vertebrae is convenient to measure
and yields a linear dimension of convenient size.
The combined length of thoracics 10-12 has there-
fore been used as the independent variable in the
present study. An obvious disadvantage of using
this measure as the independent variate is that it
is the least accurate of all the measures in the set,
and errors of measurement in the independent
variate will bias the results, even though the errors
are random.
Furthermore, length of centrum is itself a vari-
able; simple inspection shows that vertebrae are
relatively longer in Mustela than in Ursus, for ex-
ample. Therefore, index figures derived from this
common standard have no absolute value for pur-
poses of comparison. They are only approxima-
tions, their reliability depending upon the range
of variation in relative vertebral length within the
sample. Reliability is certainly great enough to
demonstrate gross deviations from the norm.
A further problem in interpreting these data is
the selection of a norm against which the index
figure can be evaluated. Femur length cannot be
judged "short" or "long" unless it is shorter or
longer than some standard femur length for the
Carnivora. Probably the best that can be done
is to use the index figure for the least specialized
representative of the Carnivora as a norm. In
Table 2 the figures for the wolverine (Gulo), whose
locomotor habits are as generalized as those of any
living carnivore, are used as a norm, the figures
being rounded off to the nearest multiple of 5.
From the table it appears that arm length is the
most conservative among the four limb segments
and foi-earm length the most variable.
These indexes correlate quite well with what is
known of the locomotor habits of the animals.
There are puzzling non-conformities (e.g., long
proximal segments in Ailurus, short arm in Vi-
verra, long fore arm associated with long thigh in
Felis leo, etc.) that cannot be explained on the
basis of existing knowledge. Disregarding these
exceptions, limb proportions appear to correlate
with locomotor types as follows in the Carnivora:
Ambulatory walking norm
Running all segments long,
especially forearm
Arboreal climbing
Type A hind legs long
Type B forearm short,
other segments norm
Digging di.stal segments short
Swimming all segments very short,
especially forearm
The bears and the giant panda, in which a short
tibia is associated with length in the other three seg-
ments, do not fit any of these categories, and this
combination is difficult to justify on a mechanical
basis. Elongated limbs are generally associated
with running, where a long stride is advantageous.
The limbs are also long in graviportal animals
(e.g., elephants, titanotheres), although the me-
chanical factors involved are unknown. The bears
Table 2. LIMB PROPORTIONS IN CARNIVORES'
N
Canis lupus 4
Canis latrans 3
Chrysocyon 1
Bassariscus 4
Nasua 1
Procyon 3
Polos 3
Ailurus 2
Ursus 4
Ailuropoda 2
Gulo 2
Maries pennarUi 1
Maries flavigularis 1
Taxidea and Mellivora 4
Lutra canadensis 3
Enhydra 2
Viverra langalunga 5
Paradoiurus 3
Herpesles 1
Croeula 1
Hyaena 1
Felis onca 2
Felis leo 4
Felis tigris 1
' V=Iength of thoracics 10
ifcll to 20. Extremely long or short= 21 or more
V L. humerus
V L. radius
V L. femur
V L. tibia
(norm =40)
(norm=50)
(norm = 40)
(norm = 40)
35
35
31
32
36
long
34
verj- long
32
long
32
long
all long; forearm very lot
27
very long
25
extremely long
25
ven,- long
>>
ven.- long
all very long; forearm
extremely long
43
norm
54
si. short
38
norm
40
norm
forearm slightly short
37
norm
43
long
31
long
24
ver>' long
hind legs long; all distal
segments long to very
long
34
long
34
ver>' long
29
ven,- long
28
verj- long
all very long, except
humerus long
39
norm
48
norm
34
long
36
long
hind legs long
36
slightly long
48
norm
34
long
37
norm
proximal segments long
32
long
39
very long
27
very long
39
norm
all long-very long,
except tibia norm
34
long
44
long
34
long
4S
short
all long, except tibia
short
40
50
38
42
all norm
norm
norm
norm
norm
41
norm
73
extremely short
37
norm
37
norm
forearm extremely short
45
short
60
short
40
norm
41
norm
forelegs short
42
norm
55
short
40
norm
53
very short
distal segments short;
tibia very short
68
very short
95
extremely short
67
extremely short
60
very short
all very short, forearm
extremely so
77
extremely short
102
extremely short (
74
extremely short
66
extremely short
all extremely short,
especially forearm
47
51
37
39
arm short
short
norm
norm
norm
42
norm
54
slightly short
39
norm
42
norm
forearm slightly short
50
short
65
very short
41
norm
46
short
all short-ver>' short,
except femur
33
long
32
very long
27
very long
36
long
all long; forearm and
thigh very long
33
long
30
verj- long
30
long
34
long
all long; forearm very
long
40
norm
51
norm
35
long
43
norm
long thigh
38
norm
42
long
33
long
39
norm
long forearm and thigh
43
norm
52
norm
36
long
43
norm
long thigh
2. Norm = 3 from norm. Lor
ig=-4 to -10.
Short= +4 to +10. Verj- long or short
36
SUMMARY OF LIMB SEGMENT RATIOS IN CARNIVORES
Ambulatory walking .
Running
Half-bound (cats) . . .
Climbing
Digging
Swimming
Mediportal types
Ursus
Aibiropoda
Humeroradial
Femorohumeral
Femorotibial
Tibioradial
Intermembral
80
radius short
95
subequal
90 +
tibia short
75 +
radius shorter
90 +
hind legs long
100 +
equal
90-
femur longer
98 +
equal
90 +
radius short
90 +
hind legs long
80-90
radius short
85 +
femur longest
85-
tibia shorter
85 +
radius shorter
85 +
hind legs longer
80-
radius shorter
90-
femur longer
95 +
subequal
75 +
radius shorter
85-
hind legs longer
80-
radius shorter
90 +
femur long
75+
tibia shortest
95 +
subequal
92 +
hind legs long
75
radius shortest
95 +
subequal
110 +
tibia longest
65-
radius shortest
80
hind legs longest
80 +
radius shorter
85
femur much
longer
70
tibia very much
shorter
96 +
subequal
90
hind legs long
77
radius much
shorter
98
equal
76
tibia much
shorter
99
equal
99
equal
400T
? 300
Ursus omerlcanus
D " arctos
A " gyos
Ailuropoda
200
150
Ailuropoda Y= 37.3 + 0.63 X
Ursus Y= -6.5 -1- 0.83 X
200
300
Humerus Length
400
500
Fig. 12. Scatter diagram, with fitted regression lines, showing length of radius and length of humerus in panda and bears.
(Dashed line=slope of 1.)
37
38
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
/
400-
300--
200-
150
Ursus omerlcanus
o " orctos
a " gyas
Ailuropoda
/
/
200
300
Femur Length
400
500
Fig. 13. Scatter diagram, with fitted regression lines, showing length of tibia and length of femur in panda and bears.
(Dashed line=slope of 1.)
and the panda are relatively slow-moving ambu-
latory walkers and lack the elongation of the meta-
podials that characterizes runners. Shortening of
the distal segments characterizes digging animals,
in which the mechanical advantage of increasing
effective power at the distal ends of the limbs is
obvious. Gregory (in Osborn, 1929) noted that
among ungulates the tibia shortens with gi-avi-
portal specialization, whereas relative radius length
either remains stationary or shortens to a less de-
gree than tibia length. This is exactly the situa-
tion in the bears and the giant panda, whose limb
proportions are those of mediportal or graviportal
animals.
Intramembral Indexes
Ratios of limb segments with respect to each
other reflect the same pattern as ratios derived
from an independent variable. They have the ad-
vantage over the preceding ratios of greater math-
ematical reliability and of widespread usage (see
A. B. Howell, 1944). Limb segment ratios of rep-
resentative carnivores are given in Table 2.
These figures are associated with locomotor
types as shown in the following summary. Several
forms (e.g., Procyon, Ailurus, Viverra, Herpestes)
do not fit well into any of the categories, and again
it must be assumed that unknown factors are in-
volved in determining the limb proportions of such
forms.
Ratios for the bears agree with those of medi-
portal or graviportal ungulates. Furthermore, this
agreement is associated with other mediportal
adaptations, such as flaring ilia and relatively slight
angulation of the limbs at elbow and knee.
The peculiar i-atios in Ailuropoda do not occur
in any other known mammal, and they often differ
from the corresponding ratios in Ursus. They are
most closely approached by those of the burrowing
mustelids. Functional lengths of humerus and
femur are equal in a very few scattered forms
{Tamandua, Icticyon, Dolichotis; A. B. Howell,
1944). Equality in length of radius and tibia is
more common but follows no pattern. Equality
in the intermembral index occurs elsewhere among
terrestrial mammals only in a few aberrant forms
(giraffe, hyenas, the extinct forest horse Hippidi-
um; A. B. Howell, 1944). I conclude that limb
proportions in Ailuropoda are attributable to fac-
tors other than mechanical requirements that
DAVIS: THE GIANT PANDA
39
400 --
5 300 --
200
Ursus americanus
D " arctos
A >
a gyas
Ailuropoda
/
/
Ailuropoda Y= -89.1 -i- 1.21 X
Ursus Y= -58.6+ 1.I6X
150
200
300
400
500
Pelvis Length
Pig. 14. Scatter diagram, with fitted regression lines, showing breadth and length of pelvis in panda and bears. (Dashed
line=slope of 1.)
selection for mechanical efficiency has been over-
ridden by some other factor or factors.
Allometry
Examination of linear measurements of the limb
bones of Ailuropoda (Table 6, p. 45) shows that
proportions vary with the absolute size of the
bones. When pairs of measurements for all indi-
viduals are plotted on scatter diagrams, clustering
of observations along a line that deviates from a
45 angle is evident for nearly all limb proportions.
This indicates that limb proportions conform to
the well-known allometric equation y = a + bx,
where z and y are the two measurements being
compared, and a and b are constants. Regression
lines were fitted to the data by the method of least
squares (Simpson and Roe, 1939).
For the limb bones of Ailuropoda the plotted
points are somewhat scattered (figs. 12, 13), indi-
cating considerable individual variation in pro-
portions. The slopes of the regression lines diverge
from unity, indicating an allometric relationship
between proximal and distal segments of the legs;
radius and tibia become increasingly short relative
to the proximal segments as total organism size
increases.
Conditions in Ursus are similar, although allom-
etry is considerably less for the radius than in
Ailuropoda. The plotted observations for all pro-
portions cluster much more closely ai'ound a straight
line, indicating relatively little individual variation.
The deviations of the regression lines from unity
are not statistically significant for either Ailuro-
poda or Ursus. The close clustering of the values,
especially for Ursus, suggests that they would be
significant in a larger sample.
Similar analyses of data on limb proportions in
other cai'nivores are available only for the domes-
tic dog. Lumer (1940) found a close correlation,
but only a very slight deviation from unity in the
slopes of regression lines, in both humeroradial
(6=1.098) and femorotibial (6=1.090) proportions
in an analysis of data from a wide variety of breeds
of dogs.
40
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
The limb girdles in the panda and bears are less
consistent than the limb segments. In the scapula
of the panda there is little correlation between
height and breadth (r=0.45, N=9). In Ursus, on
the contrary, there is a very close correlation be-
tween height and breadth of scapula (r=0.98,
N=9), but only a slight indication of allometry
(6=0.94). The pelvis shows a high correlation in
total length/breadth across ilia in both Ailuropoda
and Ursus. There is also a strong allometric rela-
tionship (6=0.75 in Ailuropoda, 6=0.57 in Ursus),
the iliac breadth becoming increasingly great as
size of pelvis increases (fig. 14).
The "law of allometry' has been tested by many
workers in a wide variety of cases, and found to be
a valid empirical representation of ontogenetic
growth relations. We may therefore postulate
that the allometric relations demonstrable in Ailu-
ropoda and Ursus reflect genetically determined
processes that are as characteristic of the species
or genus as are any morphological feature, repre-
senting what Lumer has called "evolutionary al-
lometry." The intensity of expression of such
size-dependent relationships is a function of or-
ganism size. Therefore the proportions at any
particular phylogenetic stage (strictly, at any par-
ticular organism size) may not be, and in extreme
cases certainly are not, directly related to the re-
quirements of the organism. If selection has fa-
vored increased organism size, then proportions
may become increasingly grotesque until a point
is reached where the disadvantages of mechani-
cally unfavorable proportions balance the advan-
tages of further increase in organism size.
V. CONCLUSIONS
1. The external characters of the giant panda
are basically similar to those of Ursus. Differences
from the bears are for the most part conditioned
by more fundamental differences in underlying
structures.
2. The absolute size of the giant panda is al-
most identical with that of the American black
bear.
3. Body proportions of the bears and the giant
panda differ from those of all other living carni-
vores. They resemble the proportions of medi-
portal or graviportal animals, although the mass
of the smaller bears and of the giant panda is less
than that of mediportal ungulates. It is also less
than that of the larger cats, which show no medi-
portal specializations.
4. The trunk in the giant panda is relatively
shorter than in any other known carnivore.
5. Limb proportions in the giant panda resem-
ble those of bears, but differ in some important
respects. In neither the panda nor the bears can
they be explained on the basis of functional re-
quirements.
6. Limb proportions in the panda and the bears
show indications of allometry, the distal segments
being relatively shorter in larger individuals. Pel-
vic proportions are also allometric, but scapular
proportions are not.
7. Body proportions in the pandas and bears
are not the result of selection for mechanical effi-
ciency. Rather they reflect pleiotropic correla-
tions with other features that have been altered
through natural selection.
SKELETON
Most of the literature on the mammalian skele-
ton is purely descriptive, with no real considera-
tion of the soft parts to which the bones are
intimately related in form and function, of the
functions of the bones themselves, or of the fac-
tors responsible for observed differences between
species. Comparisons are often unreal, for bones
are compared as if they were inanimate geometri-
cal forms rather than artificially segregated parts
of living organisms. As a result there has been
little attempt to evaluate differences in other than
purely quantitative terms. Even the descriptions
are often inadequate because the observer described
only what he saw. The primary objectives have
been to find "characters" on which a classification
of mammals can be based, or to reconstruct the
phylogenies of organisms or of structures. These
are important but severely limited goals.
The gross features of the skeleton are deter-
mined by heredity, conditioned by events in the
remote past; mammals have one bone in the thigh
and two in the leg because they inherit this pattern
from their remote ancestors not because it is par-
ticularly suited to the needs of mammals. Within
the limits set by this inherited framework, the pri-
mary function of the skeleton is support, and the
form and architecture of bones reflect primarily
the stresses and strains associated with this func-
tion. Each bone is also subjected to an assort-
ment of constantly varying localized stresses and
strains resulting from the action of muscles and
ligaments. Besides these mechanical factors, the
skeleton also serves as a store for calcium salts.
Consequently the architecture of a bone is far
more complex than is generally assumed, and at-
tempts to analyze bones from the engineering
standpoint have not been entirely successful (see
Wyss, 1948).
In the individual the basic features of the skel-
eton, including accumulated adaptive features
acquired during phylogeny, are determined genet-
ically. We cannot go far beyond this obvious gen-
eral statement, although Stockard (1941) and
Klatt (1941-43) made a beginning at discovering
the nature of this genetic control, and Sawin (1945,
1946) and his co-workers demonstrated gene con-
trol of morphogenetic fields in the skeleton. Scott
(1957) concluded that growth and differentiation
of the skeleton depend on two distinct processes:
(a) a length-regulating process controlled by con-
version of cartilage into bone (interstitial growth),
and (b) a robustness-regulating process that deter-
mines the thickness of the limb bones, the size of
the vertebrae, etc., and involves the activity of the
subperiosteal cellular tissue (appositional growth).
It is likewise obvious that the inherited features
of the skeleton are modified, within limits, by the
activities of the individual. This is seen, if proof
is needed, in the vertebral column of Slijper's bi-
pedal goat (Slijper, 1946), in the adaptations to
pathological conditions described by Weidenreich
(1926, 1940), and in the experiments of J. A.
Howell (1917), Washburn (1947), Wolffson (1950),
Moss (1958), and others. This non-hereditary'
factor is of unknown, but probably considerable,
importance in determining the morphology of the
bones. Howell, for example, found that in the bones
of the fore leg of the dog most or all growth in
diameter (appositional growth) is dependent on
extrinsic mechanical factors, whereas growth in
length (interstitial growth) is largely independent
of mechanical factors.
Finally, it is reasonable to assume that the ca-
pacity of the individual skeleton to respond adap-
tively to specific functional demands is inherited,
and that this capacity varies with the age of the
individual.
The description of the skeleton of the giant
panda here presented is somewhat unorthodox.
The customary detailed description of each bone
has been largely omitted; the illustrations should
supply such information. The relations between
bones and muscles, blood vessels, and nerves has
been emphasized; and mechanical factors, which
seem to have been of more than usual importance
in molding the morphology of the giant panda,
have been treated to the best of my ability. I
have aimed not merely to describe and compare,
but so far as possible to interpret.
' The muscles and other soft parts that act on the bones,
as well as the psychology that directs the basic activities of
the animal, are presumably gene-controlled. Thus even this
factor is hereditary, at second hand, so to speak.
41
42
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Fig. 15. Skeleton of Ailuropoda melanoleuca (CNHM no. 31128, adult male).
L THE SKELETON AS A WHOLE
The skeleton (fig. 15) resembles in general ap-
pearance that of a bear of similar size. The massive
skull and short vertebral column give a somewhat
non-ursid aspect to the skeleton. As in Ursus,
surface modeling on the limb bones is prominent.
The mass of the skeleton is greater than that
of a black bear of similar size. This is largely but
not entirely due to the much heavier skull (Table 3).
Table 3. WEIGHT IN GRAMS OF DRY SKELETON
Skull as
percentage
CNHM
Sex
Total
Skull of total
36758
Ailuropoda
5550
1581 29
31128
Ailuropoda
cT
6055
1583 26
44725
Ursus americanus a'
5029
818 16
18864
Ursus americanus
3690
694 19
47419
Ursus arctos. . . .
11018
1923 18
65803
Ailurus fulgens .
9
269.6
67.5 25
49895
Procyon lolor . . .
d'
384.5
67.8 18
54015
Canis lupus . . . .
9
2013
377.5 19
46078
Hyaena striata . .
2083
465 22
18855
Crocuta crocuia.
3947
864 22
For the giant panda and black bear these figures
represent about 4 per cent of total body weight.
Further analysis of weight figures shows (Ta-
ble 4) that percentages of total postcranial skele-
ton weight formed by the trunk, fore limbs, and
hind limbs are very similar in giant panda and
bears. These ratios vary considerably among the
other carnivores.
It is evident that, except for the skull, the rela-
tive proportions of total skeleton weight formed
by each of the major regions of the skeleton in
Ailuropoda do not differ significantly from those
of Ursus. This is not true of the skull, which is
extraordinarily dense in the giant panda. The
skull-postcranial ratio is quite constant at 16-19
per cent in other carnivores examined, except Ailu-
rus and the hyenas, in which the masticatory appa-
ratus is likewise exceptionally powerful.
The weight of the bones of the fore limbs is rela-
tively greater in Ailuropoda, Ursus arctos, and the
hyenas than in the other carnivores (Table 4).
Klatt and Oboussier (1951) found this likewise
true of bulldogs compared with greyhounds, al-
though the disproportion (bulldog 69 : 31, grey-
hound 61 : 39, on fresh bones) was greater than in
any of our material. Klatt and Oboussier found
a comparable disproportion in total weight (i.e.,
including soft parts) of the limbs, and an even
greater disproportion for the head. They con-
cluded that the bulldog proportions result from a
DAVIS: THE GIANT PANDA
43
Table 4. WEIGHT RATIOS IN DRY POSTCRANIAL SKELETON
Percentage of Total Postcrania!
Fore limbs : Hind limbs
Trunk
(incl. pelvis)
CNHM
36758 Ailuropoda 44
31128 Ailuropoda 46
44725 Ursus americanus 46
18864 Ursus americanus 42
47419 Ursus arclos 46
65803 Ailurus fulgens 47
49895 Procyon lotor 47
54015 Canis lupus 40
46078 Hyaena striata 43
18855 Crocuta crocuta 45
Skeleton
Fore
limbs
Hind
limbs
31
25
55
45
31
23
57
43
29
25
54
46
30
28
52
48
32
22
59
41
27
26
50
50
23
30
43
57
32
28
53
47
34
23
59
41
32
23
59
41
generalized regional effect, centered in the head
but affecting the whole forequarters.
Taylor (1935) has shown that the relative mass
of the skeleton increases, whereas relative bone
area decreases, with increasing body size in a series
of mammals. He presented data for a series of
forms ranging in size from the albino rat to the
domestic cow. Surface areas of a humerus and a
femur of an adult male giant panda and an adult
male black bear were measured according to Tay-
lor's method. Each bone was carefully covered
with adhesive tape. The tape was then removed
and weighed (the number of square centimeters
per gram of tape having been determined). This
method yielded highly consistent results on our
material. The data are given in Table 5.
In the giant panda the surface area of the hu-
merus exceeds that of the femur by 6 per cent,
whereas in the bear the reverse is true and the
area of the femur is 6 per cent greater than that
of the humerus. The surface area per gram of
bone in the bear is exactly the same as the figure
for man, as computed by Taylor; in the panda it
is slightly less, because of the greater thickness of
the walls. Taylor found that this ratio decreases
with increasing organism size from 10.6 square
centimeters per gram of bone in the rat to 0.69
in the domestic cow. The bear falls in about its
proper place in his table; in the giant panda the
long bones are heavier than would be expected in
a mammal of its size.
Thickness of the walls of long bones was meas-
ured at the center of the shaft on X-ray photo-
graphs. The walls are notably thicker in Ailuropoda
than in a bear of comparable size; the walls of the
humerus are about 30 per cent thicker, those of
the femur about 60 per cent thicker (Table 5).
The diameter of the medullary cavity is corre-
spondingly decreased in the panda, showing that
the abnormal cortical thickness results from a
slowing down of resorption rather than from in-
creased osteoblastic activity. The ulna is about
20 per cent thicker in Ailuropoda, and the tibia
about 27 per cent thicker. Such increased cortical
thickness cannot be attributed to mechanical re-
quirements; it must instead reflect a pleiotropic
effect or important differences in mineral metab-
olism.. Indeed, it is well known that thickening
the walls of a tube internally adds very little to
the strength of the tube, whereas adding the same
quantity of material to the outer surface does in-
crease its strength significantly. Increase in mus-
cle mass leads only to increase in the surface area
of bone, not to an increase in thickness (Weiden-
reich, 1922).
Table 5. SURFACE AREAS OF LIMB BONES
Bone Bone Surface Area per
weight length area gm. of bone
gms. cm. cm. 2 cm.'
Ailuropoda
Humerus 268.9 27.8 368.1
Femur 251.3 28.2 344.6
Total 520.2 712.7 1.36
Ursus
Humerus 214.6 26.3 344.6
Femur 239.8 31.6 364.9
Total 454.4 709.5 1.56
Thickness of wall
at center of shaft
mm.
6.5
8
5.5
5
44
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Fig. 16. Ground sections of compacta from middle of shaft of femur of Ailuropoda (left) and L'rsus gyas (X 100).
These measurements also indicate the existence
of regional differences in rate of bone deposition or
resorption. The walls are significantly thicker in
the hind leg than in corresponding bones of the
fore leg, and the proximal segments are relatively
thicker than the distal.
The histological structure of the compacta of the
long bones shows no differences between Ailuro-
poda and Ursus (fig. 16). The bone is typically
lamellar, with well-developed Haversian systems.
Partly destroyed Haversian systems are numer-
ous, and osteocytes are present in normal numbers.
There is no evidence of retarded internal reorgani-
zation of the bone.
Mineral metabolism involves the skeleton. The
normal diet of Ailuropoda contains quantities of
certain minerals (especially silicon) that are ab-
normal for a carnivore. It therefore seemed desir-
able to determine the relative amounts of minerals
in the bone. The following semi-quantitative spec-
trochemical analysis of bone samples from wild-
killed animals was made by the Spectrochemical
Laboratory of the University of Chicago. Obvi-
ously there is no significant difference between
them.
In summary, the skeleton of Ailuropoda is more
dense throughout than that of Ursus, due to
Ursus americanus Ailuropoda
CaO --48^^ ^45^c
MgO 0.9% 0.95%
SiOj x> .6 X X'
Sr --1200ppm ^1200 ppm
Ba -- 300ppm --300ppm
' Working curve not available, but SiOj is less than 1 %,
probably about 0.1-0.4%. Ailuropoda has less SiOa than
Ursus by a factor of 0.6.
greater thickness of the compacta. This is partic-
ularly true of the skull. The increase in quantity
of compacta cannot be attributed to mechanical
requirements. Regional differences in relative
thickness of compacta indicate that rate of bone
deposition or resorption is not uniform throughout
the skeleton. There appears to be a gradient in
which relative thickness of compacta decreases
distally.
II. MEASUREMENTS
Most of the bone measurements used in this
study, except for those of the pelvis, are given in
Table 6. These include all measurements used in
calculating ratios and proportions for the most im-
portant of the species used in this study.
Lengths of the leg bones are not greatest over-
all length, but the much more meaningful "func-
tional length" recommended by Howell. Func-
tional length is the distance between the termina
Table 6 MEASUREMENTS OF CARNIVORE SKELETONS'
AMNH= American Museum of Natural History; CM=Carnegie Museum; CNHM = Chicago Natural History Museum;
USNM = United States National Museum
Ailuropoda
melanoleuea ^ g m
CNHM w ^~
31128 c? 278
34258 285
36758 9 267
39514 277
47432' cfj 264
74269' cf 308
CM
18390 284
AMNH
110451 9 275
110452 9 265
110454 280
USNM
258423 274
259027 d' 295
259074 cf 282
259401 cf 266
259402 cf 290
259403 9 268
259076 9 238
258984 213
259400 9 243
132095 234
259075 cf 273
258834 cf 273
259029 cf 304
258836 d" 276
258425 d^
CNHM
Ursus arctos
43744 321
47419 360
84467 9j 241
Ursus ggas
49882= 9 358
63802 d' 450
27268 440
27270 293
63803 9
Ursus americanus
18864 256
44725' & 273
Ailurus fulgens
65803' 9 112
57193' d'
57211' d'
Procyon lotor
49895 d' 116
49227 d' 115
49057 d" 120
47386 d' 114
Gulo luscus
57196 9 158
74056 &
79409 d 167
Canis lupus
21207 9 246
51772 & 263
51773 9 253
54015 9 238
Skull
Spine
Fore Leg
Hind Leg
C3
^ I _
C bo
o c
0,2
250
257
246
289
2-c
NJ2
252 131 206
132
129
130
144
206
207
180
152
168
149
153
132
ii be
O C
685
665
CO
>= o
MJ3
taj3
M J3
96 164 184
92 164 160
826 105
ea c
73
bOc
fe.S
OS'S
-1
II
o 2
J E
279
209
50.5
282
212
53
224
51.2
216
55.9
277
214
53.0
273
210
57
282
222
58
314
254 131 210 154
251
133
202
143
245
126
207
145 .
170 184 266 212
276 211
254
130
193
141
.. 173 180 267 211
271 206
253
134
199
142
160 157 260 199
260 202
267
135
213
164 737
192 186 280 222
53 290 225
57
256
130
206
167 680
164 164 272 ...
57.5 280 ...
247
122
200
150
261
142
213
159 794
162 185 256 ...
52.5 285 215
58
240
125
202
159 .
229
123
172
120 .
203
106
142
100
128
129
239
124
181
124 .
224
120
167
113 .
255
138
206
145 .
253
133
142
202
215
145 .
165
255
136
149 .
131
n 163 273 204
276 203
320
152
190
155 92
!2
93 2(
)9 192 304 247
73.5 355 248
78
330
172
227
172 9;
)0
01 2:
;6 220 312 255
73.5 377 253
78
234
128
132
95 .
.. n
!6 117 204 162
249 179
332
180
.. 2f
53 222 330 283
90 402 280
93
433
225
267
232
352 336 415 345 109 519 355
116
390
208
267
221 .
3
1 301 386 305 105 464 315
107
285
153
158
125 .
2;
)3 230 346 276
...
.. 24
17 221 327 268
91 390 275
96
242
130
139
106 7<
51
81 1.
50 151 244 191
65.4 276 197
67
270
133
155
124 81
8
86 1'
72 157 268 225
70.5 318 232
73
102
53
76.5
38.5 3'
r5
40.5 (
51 57 107 83.2
115.5 107
.. 3(
)6
40 (
40.5 (
54 58 105.2 83
55 59 111 80
30 115.5 104
30.5 116.5 104.5
38
38.5
115
70.
5 75.5
3(
50
38.0 '
r5 70 110.8 110.3
134.7 136.4
113
70
76
3<
2
36.5 '
12 65 109 112
.. 130.5 127.5
116
72
76
3(
13
33 1
52.5 59 96 95.5
113.5 116
113
71
79.5
61 32
!7
35 (
59 59.5 99 101
30 118.5 121
37.5
149
82
53.5 !
56 80 139 107.5
.. 145 131.5
145
79
104
90 5i
:0
57 ;
iS 84 139 112
47 148 134
56
154
83.
5 110
95
c
)2.5 90 141 111
47.5 151 135
56
234
122
129
77
74 1;
)7 107 209 213
94 234 233
107
248
135
139
81.6 75
)5
80 ll
54 108 228 227
255 246
109
241
130
133
80.5 7f
53
76 IE
)7 110 216 210
96 241 233
104
225
120
133
76 .
69 U
)4 100 209 207
95.5 230 232
108
Pelvic measurements on p. 103.
' Zoo specimen.
45
46
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
articular surfaces of the bone. In most instances
the appropriate point on the articular surface is
either the same as that used for greatest over-all
length or can be fixed with equal precision. In a
few instances both ends of the radius, and the
distal end of the tibia the shape of the articular
surface makes it impractical to fix exactly the
proper point from which to measure, and conse-
quently the corresponding measurements are less
precise. I have measured from the approximate
center of such oblique articular surfaces. In a
study of the present kind the advantages of com-
paring functional lengths outweigh any disadvan-
tages resulting from slightly lessened precision.
For metacarpal and metatarsal length the long-
est bone was measured, regardless of which one it
happened to be. For Ailiiropoda this is meta-
carpal 4 and metatarsal 5; for all other species in
the table it is metacarpal 4 and metatarsal 4.
In measuring the scapula, height was measured
along the spine, from the glenoid cavity to the ver-
tebral border. Breadth is the distance between
two lines that are parallel to the spine and intersect
the anterior and posterior borders of the scapula.
Length of the vertebral column was measured
from the anterior border of the ventral arch of the
atlas to the posterior border of the centrum of the
last lumbar. The column of the smaller species
was still articulated by the natural ligaments, and
length was measured along the cui-ves of the artic-
ulated spine. For the larger species, in which the
bones were disarticulated, the vertebrae were laid
out in proper sequence on a flat surface, following
the natural curves of the backbone. Length was
then measured along the cui'ves.
All measurements are in millimeters.
Cranial Capacity
Cranial capacity was measured by filling the
cranial cavity with dry millet seed and then meas-
uring the volume of the millet seed in a gi'aduated
cylinder. Ten trials were made for each skull, and
the trial that gave the highest reading was re-
garded as the closest approximation to the true
cranial capacity. The difference between the low-
est and highest reading averaged less than 4 per
cent for all skulls, and in no case was it greater
than 6 per cent.
In cranial capacity, as in other basic size charac-
teristics, the giant panda resembles the American
black bear very closely.
III. THE SKULL
The skull of Ailuropoda is characterized by its
great density and by extreme development of the
sagittal crest and expansion of the zygomatic
Table 7. CRANIAL CAPACITY OF CARNIVORES
Ailuropoda melanoleuca
CNHM C.C.
31128 d" 320
36758 9 288
39514 282
Mean 297
Ursus americanus
CNHM
16027 280
18146 261
18151 310
18152 d' 313
51641 cf 312
68178 d' 327
Mean 300
Ursus arctos
CNHM
25713 412
81509 335
arches in comparison with other arctoid carni-
vores. These features are associated with very
powerful dentition and masticatory musculature.
The cranial skeleton and to a lesser extent the
facial skeleton are profoundly modified by the de-
mands of mastication. The cranium gives the
impression of having been subjected to plastic de-
formation by the temporal muscle, which has at-
tempted, so to speak, to achieve maximal volume.
Expanding to the limit in all directions, the tem-
poral muscle has displaced and compressed sur-
rounding structures to the mechanical limit on the
one hand, and to the limits of functional tolerance
on the other. The face, on the contrary, is rela-
tively unmodified except where it is hafted to the
cranium, and in the expansion of the alveolar area
in association with the enlarged cheek teeth.
The sutures between bones are almost com-
pletely obliterated in adult skulls. The bones of
the cranium are much thickened. In the parietal
region total thickness is 5 mm. (two individuals),
whereas in a skull of Ursus arctos the bone in the
same region measures 2.3 mm. and in a skull of
Ursus americanus only 1.7. The increased thick-
ness in the panda involves only the outer lamina
of the bone; the inner lamina is no thicker than in
the bears. This is likewise true of the basicranial
region: in a sectioned skull of Ailuropoda the outer
lamina of the sphenoid is 2.6 mm. thick below the
sella, whereas in a skull of Ursus americanus it is
only 0.9 mm. The difference is similar in the man-
dible; at the level of the posterior border of M2 the
body is 12.2 mm. thick from the mandibular canal
to the external surface of the bone in Ailuropoda
(3.6 mm. in Ursus americanus), and 5 mm. from
DAVIS: THE GIANT PANDA
47
the mandibular canal to the inner surface (3.4 mm.
in Ursus americanus) .
The bones of the face, on the contrary, are little
if any thicker in Ailuropoda than in Ursus.
Ailurus agrees more or less closely with the giant
panda in skull proportions. As was pointed out
by the earliest investigators, there is also a super-
ficial resemblance to the hyenas, associated with
similar masticatory requirements.
In the following description the skull of the Euro-
pean brown bear {Ursus arctos) is used as a basis
for comparison. Four adult skulls of Ailuropoda
in the collection of Chicago Natural History Mu-
seum were available for detailed examination. One
of these (no. 36758) was bisected in the sagittal
plane and cut frontally through the right auditory
region. None of these skulls shows the sutures;
these were determined on a young female skull bor-
rowed from the U. S. National Museum (USNM
No. 259076).
A. The Skull as a Whole
(1) Dorsal View
In dorsal view (norma verticalis) the skull of
Ailuropoda is dominated by the tremendously ex-
panded zygomatic arches. These form nearly a
perfect circle, compared with the triangular out-
line in Ursus and other carnivores. The primary
result of this expansion is to increase the volume
of the anterior third of the temporal fossa.
The muzzle appears to be shortened and has
often been so described. This is not true, how-
ever; the pre-optic length is nearly identical in
Ailuropoda and Ursus. The muzzle is no wider
anteriorly than in Ursus; its borders divei'ge pos-
teriorly instead of being nearly parallel as in Ursus,
but this merely reflects the broader cheek teeth of
the panda. The postorbital process on the frontal
is scarcely indicated, and in one skull it is absent.
The alveolar pocket of the tremendous second up-
per molar is conspicuous immediately behind the
floor of the orbit; this is invisible from above in
Ursus but is equally prominent in Ailurus and
Procyon. The interorbital diameter is not greater
in the bears than in the giant panda, but the post-
orbital constriction is more pronounced in the
panda, and this increases the volume of the ante-
rior part of the temporal fossa. This constriction
is reflected in the form of the brain, which in Ailu-
ropoda is much narrower anteriorly, in both trans-
verse and vertical diameters, than in Ursus. The
maximal cranial diameter is about 10 per cent
greater in Ailuropoda, and this, together with the
greater postorbital constriction, gives a character-
istic hourglass outline to the skull in dorsal view.
Thus the volume of the anterior part of the tem-
poral fossa has been increased by expansion both
laterally and medially, whereas the volume of the
posterior part of this fossa has been far less affected.
The skull of Ailurus exhibits a similar increase in
the volume of the anterior part of the temporal
fossa. In the hyenas, in which the volume of the
temporal fossa is also notably increased, it is the
posterior part of the fossa that is expanded by pos-
terior extension. The reasons for this difference
between herbivorous and carnivorous forms are
discussed later (see p. 155).
The horizontal shelf formed by the posterior root
of the zygoma is not wider in Ailuropoda than in
Ursus, but it is carried farther forward along the
ventral border of the arch, thus increasing the ar-
ticular surface of the glenoid cavity on its inferior
surface and the area of origin of the zygomatico-
mandibular muscle on its superior surface. There
are conspicuous muscle rugae, barely indicated in
Ursus, on the inner face of the posterior half of
the zygoma.
The sagittal crest appears to have a conspicuous
sagittal suture, but the juvenile skull shows that
this is actually the first suture to close, and that the
"suture" in the adult results from secondary up-
growth of the frontals and parietals. The smoothly
curved outline of the lambdoidal crest contrasts
with the sinuous crest seen in Ursus, Ailurus, and
Procyon; it reflects the posterior expansion of the
temporal fossa.
(2) Lateral View
In norma lateralis (fig. 17) the skull of the panda
contrasts sharply with the bears in the facial angle
as measured from the Frankfort horizontal. In
Ursus the toothrow is depressed from the Frank-
fort horizontal at an angle of about 22, whereas
in Ailuropoda these two lines are nearly parallel.
Reference to the ventral axis of the braincase re-
veals, however, that the angle formed by the tooth-
row is nearly identical in Ailuropoda and Ursus.
Actually the position of the orbit is depressed in
Ailuropoda, as a part of the over-all expansion of
the temporal fossa, and therefore the Frankfort
horizontal is misleading in this animal.
The strongly convex dorsal contour of the skull
increases the area of the temporal fossa dorsally.
At the same time the vertical diameter of the mas-
seteric fossa of the mandible is much greater than
in Ursus. Thus the whole postorbital part of the
skull appears expanded, and the skull has a trape-
zoidal outline when viewed from the side.
The margin of the nasal aperture in the panda
curves sharply dorsally, its dorsal third lying at a
right angle to the long axis of the skull. Behind
48
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Crista orbitalisi sup.
For. ethmoideum
For. aptiaim
Fissura orbiialis
M. temporalis
Prof postorbitalis IfrotUalis]
Fossa musculans
Fossa lammalis
For. injTaorbitalis
I M pterygoideus int
M pterygoideus ext
For. ovale
Can. palatina posl. mitior
Crista orbitalis inj.
For. spkeuopatatinum *
Can. pterygopalatinum
Meatus aruxtieus
exlernus
Proc. paroccipitalis
Proc. masloideus
For. poslgtenoideum
Fig. 17. Skull of Ailuropoda seen from left side (norma lateralis).
the nasal aperture the surface of the nasal and
premaxillary bones shows a pattern of shallow
grooves, in which lie the terminal ramifications of
the infraorbital and external nasal vessels, and
small foramina through which nutrient twigs from
these vessels entered the bone. The infraorbital
foramen is small and less elliptical in cross section
than in Ursus. Below and in front of the orbit the
anterior root of the zygomatic arch bulges forward
conspicuously. The postorbital process of the jugal
is less prominent than in the bears, in which it
reaches its maximal development among the Arc-
toidea.
The temporal fossa in Ailuropoda is relatively
enormous, in keeping with the size of the temporal
muscle. Its anteroventral boundary, separating it
from the orbit, is well marked by the superior or-
bital ridge. Anteroventrally the fossa is provided
with about three well-developed muscle ridges,
paralleling the superior orbital ridge; in Ursus cor-
responding muscle ridges are present, but scarcely
more than indicated; in Ailurus there is a single
ridge in old adults. In the upper posterior part
of the fossa, near the juncture of the sagittal and
lambdoidal crests, is a conspicuous nutrient fora-
men; a similar foramen is present in the bears but
is lacking in other arctoids.
In Ailuropoda the infratemporal fossa is sepa-
rated from the orbit above by the well-marked
inferior orbital ridge throughout most of its length.
Behind the orbital fissure it is separated from the
temporal fossa by an indistinct elevation extend-
ing from the superior orbital ridge in front of the
orbital fissure to the anterior lip of the glenoid
fossa. The infratemporal fossa is relatively small.
The anterior half of the infratemporal fossa con-
tains the entrance to the infraorbital foramen, the
common foramen for the sphenopalatine (spheno-
palatine artery and nerve; nasal branches of sphen-
opalatine ganglion) and pterygopalatine (descend-
ing palatine artery and nerve) canals. These exit
by separate foramina in Ursus and other carni-
vores, but are combined in Ailurus; they have
undoubtedly been crowded together in the two
pandas by the enlarged maxillary tuberosity. The
posterior half of the fossa, from which the ptery-
goid muscles arise, exhibits muscle rugosities. The
areas of origin of the pterygoid muscles are sharply
marked on the bone. The area of pterygoid origin
is much reduced, both vertically and horizontally,
as compared with Ursus.
In Ailuropoda the foramen rotundum (maxillary
branch of trigeminus) is confluent with the orbital
fissure, although the identity of the two openings
is usually indicated by a low ridge and on one side
DAVIS: THE GIANT PANDA
49
of one skull there is a paper-thin partition sepa-
rating them. This is a feature in which Ailuro-
poda differs from all other canoids; it is associated
with the general crowding together of non-masti-
catory structures in the skull. Ailuropoda also
lacks an alisphenoid canal, which is present in Ur-
sus. In forms having an alisphenoid canal (Cani-
dae, Ursidae, Ailurus) the foramen rotundum is
situated within the canal; in Ailurus it is sepa-
rated from the orbital fissure only by a thin sep-
tum, but the two are some distance apart in the
dogs and bears. In forms lacking an alisphenoid
canal (Procyonidae, Mustelidae), the foramen and
the orbital fissure are separated by a thin septum.
In Ursus the vertical diameter of the infratem-
poral fossa is much greater than in Ailuropoda.
This is also true in Cants but not in the procyo-
nids, in which the relatively much larger orbit
encroaches on it. Reduction of the infratemporal
fossa in Ailuropoda is correlated with the more
ventral position of the eye, and thus secondarily
with the ventral expansion of the temporal fossa.
The tremendously enlarged maxillary tuberosity,
associated with the enlargement of the molar teeth,
further reduces the volume of the fossa.
The Orbit. The orbit in Ailuropoda, as in
other arctoids, is poorly defined on the skull ; only
the medial wall is entire. The orbit is an elongate
cone with the base formed by the incomplete bony
ring of the eye socket (completed by the orbital
ligament), and the apex by the orbital fissure. On
its medial wall the dorsal and ventral boundaries,
separating the orbit from the temporal fossa above
and the infratemporal fossa below, are well marked
by the superior and inferior orbital ridges. These
ridges are less prominent in other arctoids. Else-
where the boundaries of the orbit are poorly
marked on the skull; because of the feebly devel-
oped postorbital processes on both frontal and
jugal, even the anterior limits are poorly indicated
in Ailuropoda as compared with those of other
arctoids.
The orbit is rotated slightly ventrad as com-
pared with that of Ursus. Its long axis (from the
orbital fissure to the center of the eye socket)
forms an angle of about 10 with the long axis of
the skull in Ursus, whereas in Ailuropoda the axes
are parallel. At the ventral boundary of the or-
bital opening there is a prominent crescent-shaped
depression, which in life lodges a cushion of extra-
ocular fat.
The lacrimal fossa, which lodges the lacrimal
sac, is a large funnel-shaped pit at the antero-
medial corner of the orbit. The nasolacrimal canal
opens into the bottom of the fossa. The canal is
only a millimeter or two long, opening almost at
once into the nasal cavity, immediately beneath
the posterior end of the maxilloturbinal crest. Ur-
sus is unique in having the nasolacrimal canal open
into the maxillary sinus. Immediately behind the
lacrimal fossa is a shallow pit, the fossa muscu-
laris, in which the inferior oblique muscle of the
eye arises; the thin floor of this pit is usually broken
through on dry skulls, and then resembles a fora-
men. In Ursus and other arctoids the lacrimal
fossa is much smaller than in Ailuropoda, but
otherwise similar. The fossa muscularis in Ailu-
rus is very similar to that of Ailuropoda; in Ursus
it is relatively enormous as large as the lacrimal
fossa and several millimeters deep. The fossa
muscularis is completely wanting in the Canidae
and Procyonidae.
Three foramina in a row, about equidistant from
each other, pierce the medial wall of the posterior
half of the orbit. Each leads into the cranial fossa
via a short canal directed posteriorly, medially,
and ventrally. The most anterior is the ethmoi-
dal foramen, which conducts the external eth-
moidal nerves and vessels into the anterior cranial
fossa. Behind this is the optic foramen (optic
nerve, ophthalmic vessels), and most posteriorly
and much the largest is the combined orbital
fissure and foramen rotundum (oculomotor,
trigeminal, trochlear, and abducens nerves; anas-
tomotic and accessory meningeal arteries; orbital
vein). Except for the confiuence of the orbital
fissure and foramen rotundum, which is peculiar
to Ailuropoda, the pattern of these three foramina
is similar in all arctoids. Most variable is the eth-
moidal foramen, which differs in size among the
genera and may be characteristically multiple
(e.g., in Canis). The foramen ovale, in forms in
which it is separate from the orbital fissure, trans-
mits the third (mandibular) branch of the tri-
geminus and the middle meningeal artery.
The zygomatic arch functions in the origin of
the temporal fascia from its superior border, the
temporal and zygomaticomandibular muscles from
its internal surface, and the masseter from its in-
ferior surface. Its anterior root lies over the first
upper molar (over the second molar in Ursus), its
posterior root over the glenoid fossa; the arch is
therefore important in resolving the forces gener-
ated during mastication. As pointed out above,
the anterior part of the arch is expanded laterally,
which increases the volume of the anterior third
of the temporal fossa. In lateral view the arch is
straighter than in Ursus and other arctoids. Its
posterior half is much extended dorsally, which
increases the available area of origin for the zygo-
maticomandibularis muscle. The whole structure
50
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
For. nuiritium
For. palatinum ant. med.
Fossa palatina
For. palatinum ant.
Sulcus palatinus
For. palatinum post.
For. palatinum post
For. palatinum
Spina nasalis post:
Fotsa nasopharyngea
Semican. M. tensor-
tl/mpani
Semican. tubae
, . audilirae
Can. chordae tympani-
For. postglenoideum
For. lacerum post.
Proc. mastoideus
M. masseter
M. z>'gomatico-
mandibularis
Incisura palatina
M. pterj'goideus
ext.
For. ovale
Fossa }nandiimlaris
Hamulus
plerygoideus
Proc. postglenoideus
-.^featiis acusticus at.
M. stemomastoideus
For. slylomasloideum
Fossa hyoidea
Proc. paroccipitalis
M. digastricus
For. hypoglossum
For. mastoideum
Capsula articularis
M. longus capitis
M. rectus capitis ventralis
Fig. 18. Skull of Ailuropoda seen from below {norma ventralis).
is extraordinarily massive. The anterior i"oot is
bulky but relatively thin-walled, since it is exten-
sively excavated internally by the maxillary sinus.
It bulges forward anteriorly, and posteriorly forms
the floor of the orbit for a short distance before
passing into the alveolar pocket of the second
molar; the infraorbital canal is thus considerably
lengthened posteriorly. The posterior root of the
arch is expanded posteriorly to accommodate the
large mandibular (glenoid) fossa; it has encroached
considerably on the space between the postglenoid
and mastoid processes, in which the external audi-
tory meatus lies, and the meatus is consequently
much compressed.
(3) Ventral View
In ventral view {norma ventralis, fig. 18) the
facial region is dominated by the massive denti-
tion, the cranial region by the immense mandib-
ular fossae.
It has often been stated that the palate extends
farther posteriorly in Ursus than in Ailuropoda,
but this is an illusion created by the enlarged teeth
of the latter. In relation to the anterior end of the
braincase, the palate actually extends farther pos-
teriorly in the panda. The lateral borders of the
palate are parallel, as in Urstis; in other arctoids
they diverge posteriorly. The anterior palatine
foramina, which transmit nerves, vessels, and the
DAVIS: THE GIANT PANDA
51
incisive duct, are situated in the posterior part of
the large palatine fossa as in other arctoids. There
is a median nutrient foramen between the fossae
anteriorly, and a small median anterior pala-
tine foramen (large in Ursus and procyonids)
opening into a minute canal that arches back
through the anterior part of the bony septum, lies
between the fossae posteriorly. A shallow gi'oove,
the sulcus palatinus in which the anterior pala-
tine artery lay, connects each anterior palatine
foramen with the posterior palatine foramen,
which is situated at the level of the first molar
and represents the outlet of the pterygopalatine
canal. Immediately behind the posterior palatine
foramen, at the level of the second molar, is a
much smaller opening, the foramen palatina
posterior minor. In other arctoid carnivores
this foramen (often several) connects directly with
the pterygopalatine canal, but in Ailuropoda, be-
cause of the immense development of the second
molar, its canal comes to the surface briefly as a
groove on the lateral wall of the choana (fig. 20),
then re-enters the bone and finally emerges several
millimeters behind the entrance to the pterygo-
palatine canal (fig. 18). A shallow groove, not
seen in other arctoids, passes posteriorly from the
posterior palatine foramen to the palatine notch
(occasionally closed to form a foramen). As in
other arctoids, the posterior border of the palate
bears a prominent median spine.
The choanae (posterior nasal apertures) are
separate, the bony septum formed by the vomer
extending to (dorsally beyond) the posterior bor-
der of the palate. There is much variation in the
posterior extent of this septum in arctoids. In
Ursus, representing the opposite extreme from
Ailuropoda, the septum ends far anteriorly at
about the juncture of the middle and posterior
thirds of the palate, and the posterior third of the
nasopharyngeal meatus is accordingly undivided.
Other genera are intermediate between Ailuropoda
and Ursus in the posterior extent of the septum.
The nasopharyngeal fossa, situated behind
the choanae and between the pterygoid processes,
is absolutely and relatively wider than in Ursus.
The anterior half of the roof of the fossa bears a
prominent median keel, the presence and degree
of development of which varies with the posterior
extent of the septum. The pterygoid processes
present nothing unusual.
The mandibular (glenoid) fossa is the key
to other modifications of the skull in Ailuropoda.
The transverse cylindrical mandibular articulation,
limiting jaw action to a simple hinge movement
vertically and a very restricted lateral move-
ment horizontally, is a carnivore heritage that is
ill-adapted to the feeding habits of this animal.
In Ailuropoda the transverse diameter of the fossa
is much greater than in other arctoids. This di-
mension amounts to 30 per cent of the basal length
of the skull, while in other arctoids it ranges be-
tween 15 and 20 per cent, only slightly exceeding
20 per cent even in Ailurus. The increase in the
length of the fossa in Ailuropoda has taken place
wholly in the lateral direction; the medial ends of
the two mandibular fossae are no closer together
than in Ursus.
The articular surfaces of the medial and lateral
halves of the fossa in Ailuropoda are in quite dif-
ferent planes. In the medial half the articular
surface is almost wholly posterior (against the an-
terior face of the postglenoid process), while
laterally the articulation is wholly dorsal (against
the root of the zygomatic arch). Transition be-
tween these two planes is gradual, producing a
spiral fossa twisted through 90. The form of the
fossa is similar, though less extreme, in Ursus and
other arctoids. The mechanical significance of this
arrangement is discussed below.
The Basioccipital Region. The basioccipital
region in Ailuropoda, like other parts of the skull
not directly associated with mastication, is com-
pressed. It is somewhat shorter (about 5 per cent)
anteroposteriorly than in Ursus, and since in addi-
tion the postglenoid process is expanded posteri-
orly and medially, the structures in this region
(foramina, auditory bulla) are considerably crowded
together. It is noteworthy that the areas of attach-
ment of the rectus capitis and longus capitis mus-
cles have maintained their size, partly at the ex-
pense of surrounding structures.
The foramen ovale (mandibular branch of tri-
geminus; middle meningeal artery) occupies its
usual position opposite the anterointernal corner
of the mandibular fossa. There is no foramen
spinosum, since as in carnivores in general the
middle meningeal artery passes through the fora-
men ovale; the foramen spinosum is sometimes
present in Canis (Ellenberger and Baum, 1943). A
small foramen situated dorsomedially at the mouth
of the foramen ovale opens into a canal that runs
medially and anteriorly through the cancellous
bone of the basicranium to a point beneath the
hypophyseal fossa, where it meets its mate from
the opposite side. This canal apparently contained
a nutrient vessel; its counterpart was found in
Ursus, but not in other arctoids.
A single large opening, the entrance to the ca-
nalis musculotubarius, is situated at the ante-
romedial corner of the bulla. The canal is partly
divided by a prominent ventral ridge into a lateral
semicanalis M. tensoris tympani and a medial
52
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
semicanalis tubae auditivae. The foramen
lacerum medium, which normally lies just medial
to the musculotubular canal, is usually wanting
in Ailuropoda.^
Laterad of the musculotubular canal, at the
medial border of the postglenoid process, is an
irregular longitudinal slit, the canalis chordae
tympani (canal of Hugier), which transmits the
chorda tympani nerve. The position of this open-
ing is the same as in Ursus (and arctoids in gen-
eral), but in Ailuropoda it is somewhat deformed
by the enlarged postglenoid process.
The foramen lacerum posterior, which in
Ailuropoda includes the carotid foramen, is situ-
ated at the posteromedial corner of the bulla. It
transmits the ninth, tenth, and eleventh cranial
nerves, the internal carotid artery, and veins from
the transverse and inferior petrosal sinuses. The
posterior carotid foramen, through which the
internal carotid enters the skull, is situated in the
anterior part of the lacerated foramen ; this is true
also of the Ursidae and Ailurus. In other carni-
vores (Procyonidae, Mustelidae) the carotid fora-
men is removed from the lacerated foramen, lying
anterior to the latter along the medial wall of the
bulla. Segall (1943) found the positional relations
of the posterior carotid foramen to be consistently
correlated with recognized family groupings among
the Arctoidea.
The postglenoid foramen, in the posterior
wall of the postglenoid process near the external
auditory meatus, connects the temporal sinus (in-
tracranial) with the internal facial vein (extra-
cranial). The foramen is smaller and more later-
ally situated than in Ursus.
Laterad of the posterior lacerated foramen, and
bounded by the bulla anteriorly and medially, the
mastoid process laterally, and the paroccipital
process posteriorly, is a pit. This pit, a conspic-
uous element of the basicranium, is not present in
man and does not seem to have been named. I
propose to call it the hyojugular fossa (fossa
hyojugularis) . The stylomastoid foramen (fa-
cial nerve, auricular branch of vagus nerve, stylo-
mastoid artery) lies at the anterolateral comer of
the fossa; a conspicuous groove, which lodges the
' In carnivores the foramen lacerum medium (anterior of
some authors) transmits chiefly a venous communication
between the pharyngeal veins extracranially and the caver-
nous sinus intracranially. It also carries an anastomotic
twig between the ascending pharyngeal artery (extracranial)
and the internal carotid; this anastomotic artery is of con-
siderable size in the cats, but in the pandas, bears, and pro-
cyonids it is minute or absent. In Ursus the foramen lac-
erum medium is larger than the canalis musculotubarius,
and two openings, the outlet of the carotid canal posteriorly
and the entrance to the cavernous sinus anteriorly, are vis-
ible within it.
facial nerve, runs laterad and ventrad from the
foramen to pass between the postglenoid and mas-
toid processes. The hyoid fossa, at the bottom
of which the hyoid articulates with the skull, lies
in the fossa immediately behind and mesad of the
stylomastoid foramen, from which it is separated
by a thin wall. Farther posteriorly (sometimes on
the crest connecting the paroccipital process with
the bulla) is a foramen that transmits a branch of
the internal jugular vein that passes to the infe-
rior petrosal sinus.
The hyojugular fossa is almost identical in Ur-
sus, except that it is deeper and more extensive
posteriorly. In Ailurv^ it is widely open poste-
riorly, between the mastoid and paroccipital proc-
esses. The fossa tends to disappear when the bulla
is gi-eatly inflated (in procyonids, except Nasua),
but it is present in Cants.
The hypoglossal (condyloid) foramen (hypo-
glossal nerve, posterior meningeal artery) lies be-
hind and slightly mesad of the foramen lacerum
posterior. In Ursus it is usually connected with
the foramen lacerum posterior by a deep groove.
A similar groove is present in Ailurus but not in
other arctoids.
The mastoid process functions in the insertion
of the lateral flexors of the head on its posterior
surface, and in the origin of the digastric muscle
on its medial surface. The process closely resem-
bles the corresponding structure in Ursus but pro-
jects much farther ventrally than in the latter.
It is a powerful tongue-like projection, directed
ventrally and anteriorly, extending far below the
auditory meatus. The process is strikingly similar
in Procyon but is much smaller in other procyo-
nids. It is also small in Ailurus and Canis.
The paroccipital process, which functions in
the origin of the digastric muscle, is much smaller
than the mastoid. As in Ursus, it is a peg-like
projection connected by prominent ridges with the
mastoid process laterally and the bulla antero-
medially. In forms with inflated bullae (e.g., Pro-
cyon, Canis) the bulla rests against the anterior
face of the paroccipital process.
The bulla is described in connection with the
auditory region (p. 318).
(4) Posterior View
In posterior view (fig. 19) the outline of the skull
has the form of a smooth arch; the constriction
above the mastoid process seen in Ursus and other
arctoids is not evident. To this extent the nuchal
area is increased in Ailuropoda. The posterior sur-
face of the skull serves for the insertion of the
elevators and lateral flexors of the head and bears
the occipital condyles.
M. clavotrapezius
M rhomboideus
M. splenius
M. rectus capitis dorsalis medius-
Crista lamboidi
Mm. biventer cervicus et complexus
M rectus capitis dorsalis major
For. masioideum
Proe. muloideus
Proe, paroccxpilalis'
M. rectus capitis dorsalis minor
M. cleidomastoideus
Membrana atlantooccipilalis poelerior
Capsula articuiaris
M. obliquus capitis anterior
M. stemomastoideus
M. rectus capitis lateralis
M. longissimus capitis
'Membrana teclaria \ ^^SIP' fcaput ventralis)
~^M. stemomastoideus
'M. digastricus
Fig. 19. Skull of Ailuropoda seen from rear.
Sinus 1
Far. efhmoideum
Fossa eerebralis
Sinus 2
Fossa olfactoria
iMmina eribrosa
Sinus I,
Tentorium otaeum
Fossa cerebelli
Sinus sagitUUit
Elhmoturbinalia
inus transKTSut
(pars supj
Sasoturlnnale
MaxillolUTbtnale
For. paUuinum
ant.
For. palalinum
med. anl.
Sinus
temporalis
Sinus
transtersus
(pars tn/J
minor
Fossa hvpophyseos'
Dorsum seUae '
'iij- alare
For. condyloideum
Porus aeusticus int.
Fig. 20. Sagittal section of skull of Ailuropoda slightly to left of midline.
53
54
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
In Ailuropoda the peripheral area of muscular
attachment is sharply set off from the central con-
dylar area by a ridge that runs dorsad from the
medial border of the paroccipital process and then
curves mesad above the condyle. This ridge marks
the attachment of the atlanto-occipital articular
membrane; it is not so well marked in other arct-
oids. A median nuchal line, prominent in most
arctoids, runs vertically from the foramen mag-
num to the junction of the lambdoidal and sagittal
crests, separating the nuchal area into right and
left halves.
The area of muscular attachment is rugose, and
is punctured with numerous nutrient foramina. A
conspicuous scar near the dorsal midline, seen in
all except the smallest arctoids, marks the insertion
of the biventer cervicis and complexus muscles.
The mastoid foramen (meningeal branch of pos-
terior auricular artery; vein from transverse sinus)
lies directly above the paroccipital process.
The condylar area is relatively smooth, and the
condyloid fossae present an excavated appearance
because of the posterior position of the paroccipital
and mastoid processes. The occipital condyles
are more obliquely placed than in Ursus, their
long axis forming an angle of about 45 with the
vertical compared with about 25 in Ursus. The
condylar area is interrupted at the ventral border
of the foramen magnum, as it is in Ailurus. This
condition is usual, but not invariable, in Ursus.
In procyonids and canids the condylar area is al-
ways carried across as a narrow isthmus below the
foramen magnum. In Ailuropoda the form of
the foramen magnum varies from a transverse
oval to almost square.
(5) Internal View
A sagittal section through the skull of Ailuro-
poda (fig. 20) reveals the nasal cavity, the sinuses,
and the cranial cavity.
Nasal Cavity. The nasal cavity is high, nar-
row, and elongate in the arctoid Carnivora. This
is especially evident in the Ursidae. In Ailuropoda
the nasal cavity is slightly higher (index .14) than
in Ursus (index .10-.12), and slightly shorter (in-
dex .41 vs. .45-.51). In Ailurus the relative height
is the same as in Ailuropoda, but the cavity is
shorter (index .37).
The structures of chief interest in the nasal cav-
ity are the turbinates, consisting of three elements:
the maxilloturbinals, the nasoturbinals, and the
ethmoturbinals. These complex structures were
described in detail for various Carnivora by Paulli
(1900), and again by Anthony and Iliesco (1926).
In some respects, particularly with reference to
the ethmoturbinals, it is difficult to reconcile these
two studies. Paulli worked chiefiy from frontal
sections of the skull, made immediately anterior
to the cribriform plate, while Anthony and Iliesco
apparently worked from sagittal sections of the
skull.
The maxilloturbinal (fig. 20) is situated in the
anterior part of the nasal cavity, which it nearly
fills. It is kidney-shaped, much higher (45 mm.)
than long (30 mm.), and its vertical axis is inclined
posteriorly at an angle of 20. It lies entirely an-
terior to the ethmoturbinals. The maxilloturbinal
is attached to the lateral wall of the nasal cavity
by a single long basal lamella, which runs antero-
posteriorly in a slightly sinuous line about parallel
to the long axis of the skull. The line of attach-
ment extends on the premaxilla and maxilla from
near the anterior nasal aperture to a point several
millimeters caudad of the anterior border of the
maxillary sinus. The basal lamella promptly
breaks up into an extremely complex mass of rami-
fying branches that make up the body of the
maxilloturbinal.
In the Ursidae, according to Anthony and Ili-
esco, the maxilloturbinal is characterized by its
great dorsoventral diameter and its extremely rich
ramification; Ailuropoda exceeds Ursus in both.
According to these authors the Mustelidae resem-
ble the bears in the height of the maxilloturbinal
and its degree of ramification, although it may be
added that in these the upper ethmoturbinals over-
hang the maxilloturbinal. In the Canidae and
Procyonidae this element is much longer than
high, is less complex, and is overhung by the upper
ethmoturbinals. In Ailurus it is high (height/
length ratio 1) as in Ailuropoda and the Ursidae
but is overhung by the ethmoturbinals; its lamina
of origin differs from that of all other arctoids in
curving ventrad at a right angle to the axis of the
skull, reaching the floor of the nasal cavity at the
level of PMl
The nasoturbinal in Ailuropoda (fig. 20) is, as
in other arctoids, an elongate structure situated
in the dorsal part of the nasal cavity. It arises
from the upper part of the anterior face of the crib-
riform plate and extends forward, above the maxil-
loturbinal, to within a few millimeters of the ante-
rior nasal aperture.
The ethmoturbinal (figs. 20, 21) is very sim-
ilar to that of Ursus. As in other carnivores it is
composed of a medial series of plate-like out-
growths (endoturbinals, internal ethmoturbinals)
from the anterior face of the cribriform plate, and
a similar more lateral series (ectoturbinals, exter-
nal ethmoturbinals), that together fill the posterior
part of the nasal cavity. The whole structure
constitutes the ethmoidal labyrinth. The rela-
DAVIS: THE GIANT PANDA
55
VOME,
Ailuropoda
Ursus
Nasua
Fig. 21. Frontal section through turbinates, just anterior to cribriform plate. Roman numerals refer to endoturbinals,
Arabic numerals to ectoturbinals. (Diagrams for Ursus and Nasua from Paulli.)
tions of these elements are best seen on a frontal
section made immediately in front of the cribri-
form plate (fig. 21).
The endoturbinals number four, the typical
number for all Carnivora except the Procyonidae.
In the latter, according to Paulli, the fourth endo-
turbinal has split into three to produce a total of
six. It is impossible to decide, on the basis of the
section available to me, how many olfactory scrolls
the endoturbinals divide into in Ailuropoda. It is
apparent, however, that the complexity is greater
than in the Ursidae, in which there are seven.
The ectoturbinals number nine, as in the Ursi-
dae and Procyonidae. Except for Meles, in which
there are 10 (Paulli), this is the largest number
known for any carnivore. Ailuropoda further re-
sembles the Ursidae and differs from the Procyoni-
dae in having the first eight ectoturbinals situated
between endoturbinals I and II, and in having the
ectoturbinals arranged in a median and an exter-
nal series, a long one alternating with a short one
to produce the two series.
Anthony and Iliesco state that there are seven
or eight endoturbinals and that "on peut estimer
que les Ours possedent plus de 40 ethmoturbinaux
externes." These figures are obviously based on
a quite different, and I believe less careful, inter-
pretation than Paulli 's.
Paranasal Sinuses. The paranasal sinuses
are evaginations of the nasal cavity that invade
and pneumatize the surrounding bones of the
skull, remaining in communication with the nasal
cavity through the relatively narrow ostia. The
cavities lying on either side of the dorsal midline
are separated by a vertical median septum. The
occurrence, extent, and relations of the individual
sinus cavities vary greatly among mammals, often
even among individuals, and hence topography is
an unsafe guide to homologies. The cavity in the
frontal bone of many mammals, for example, is
not always homologous, and therefore cannot be
indiscriminately referred to as a "frontal sinus."
Paulli found that the relations of the ostia to the
ethmoidal elements are constant, as would be ex-
56
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
pected from the ontogenetic history, and he there-
fore based his homologies on these. He rejected
the descriptive terminology of hviman anatomy as
unusable in comparative studies, and substituted
a system of numbers for all except the maxillary
sinus. His terminology has been followed here.
The dorsal sinuses are enormous in Ailuropoda
(fig. 20), far exceeding those of any other carnivore.
At the dorsal midline they separate the relatively
thin true roof (inner lamina) of the cranial cavity
from a much heavier false roof (outer lamina) situ-
ated above it. Intrusion of the sinuses into the
supracranial area greatly increases the area of the
temporal fossa.
The relations of the ostia to the ethmoidal ele-
ments cannot be determined without cutting the
latter away. The single bisected skull available
to me could not be mutilated in this way, but simi-
larity between the sinuses of Ailuropoda and Ur-
sus is so close that there can be no doubt as to
nomenclature. As in Ursus, there is no communi-
cation between the sinuses.
Sinus I, which occupies the frontal region, is
much longer, higher, and wider than in Ursus.
It is responsible for the characteristic convex fore-
head of the giant panda. The posterior wall of
the cavity lies at the level of the postorbital proc-
ess, as in Ursus, and from here the sinus extends
forward into the base of the nasals. Its lateral
wall is formed by the outer wall of the skull. The
large oval ostium in the floor of the cavity opens
into the nasal cavity just anterior to the first endo-
turbinal. None of the ectoturbinals extends into
this cavity. In Ursus the corresponding cavity
is narrower, the maxillary sinus lying laterad of
it, and a leaf of the first ectoturbinal projects
through the ostium into the cavity.
Sinus 1 is a small cavity, measuring only about
15 mm. in length by 20 mm. in height, lying above
the olfactory fossa some distance behind sinus I.
It is surrounded by sinus 2 on all sides except ven-
trally. The small round ostium is situated in the
floor. In the skull that was dissected this cavity is
asymmetrical ; it was present on the right side only.
Sinus 2 is by far the largest of the sinuses. It
begins at the level of the postorbital process and
extends back through the frontal and parietal
bones nearly to the occiput. It is very irregular,
with numerous out-pocketings and partial septa.
The long slit-like ostium lies in the extreme ante-
rior part of the cavity, and as in Ursus a leaf of
one of the ectoturbinals projects through the os-
tium into the sinus.
Sinus IV (sphenoidal sinus of authors) is a large,
irregular cavity in the presphenoid. The ostium
is situated in its anterior wall, and as in Ursv^ the
posterior end of the last ectoturbinal projects
through the ostium into the cavity.
The maxillary sinus lies almost entirely in the
maxillary root of the zygomatic arch, a condition
that is unique among carnivores. It is situated
farther laterad than in Ursus and other arctoids.
This hollowing out of the zygomatic root makes
possible a considerable increase in bulk without
adding appreciably to its weight. The sinus is an
irregular cavity lying directly above the posterior
end of the fourth premolar, the first molar, and
the anterior end of the second molar. It opens
into the nasal cavity, immediately behind and be-
low the crest of the maxilloturbinal, by a much
smaller ostium than in Ursus.
Thus there are five pairs of pneumatic cavities
in the skull of the giant panda. Although these
greatly exceed the corresponding cavities of Ursus
in size, the arrangement and relations are very
similar. Ursus has an additional small cavity in
the roof of the skull; in Ailuropoda the area it
occupies has been taken over by sinus 2, and this
enormous sinus has almost absorbed sinus 1.
In other arctoids pneumatization of the skull is
much less extensive in number of sinuses and in
the extent of the individual sinuses. In the Mus-
telidae only the maxillary sinus is present, but
other arctoids also exhibit at least some pneumati-
zation in the frontal region. Ailurus has the same
cavities as Ailuropoda, but sinus 2 is much less
extensive, extending back only to the level of the
optic foramen.
Paulli generalized that the extent of pneuma-
ticity is dependent on the size of the skull, and
pointed out that this is borne out in large vs. small
breeds of dogs. Another over-riding factor obvi-
ously has operated in the pandas. In Ailurus the
absolute size of the skull compares with that of
Procyon, but the sinuses are more extensive. In
Ailuropoda the skull is about a third smaller than
that of Ursus arctos, but the dorsal and lateral
sinuses are much larger. The secondary factor in
pandas is a mechanical one.
It is well known that the sinuses develop as
evaginations of the walls of the nasal cavity, and
that with increasing age these out-pocketings grad-
ually invade the surrounding bone. The process
is called "pneumatic osteolysis," but the nature
of pneumatic osteolysis is unknown. In Su Lin
(age 16 months, all permanent teeth in place)
sinus 2 had not yet invaded the parietal; it termi-
nated at about the fronto-parietal suture. In this
animal, sinus I in the nasofrontal region also falls
short, by about 20 mm., of its adult anterior ex-
tension. The vertical height of both these cavi-
ties, on the other hand, is as great as in the adult.
DAVIS: THE GIANT PANDA
57
Thus considerable peripheral growth takes place
in the larger sinuses after essentially adult skull
size has been attained.
Cranial Cavity. The cranial cavity (fig. 20)
is a mold of the brain, and in the panda it differs
far less from the typical arctoid condition than do
other parts of the skull. The cavity is divided
into the usual three fossae: olfactory, cerebral,
and cerebellar (anterior, middle, and posterior of
human anatomy).
The olfactory fossa is much reduced in diam-
eter as compared with that of Ursus, but is other-
wise very similar. It houses the olfactory bulbs.
The floor of this fossa is on a higher level than the
remaining cranial floor. In the midline of the floor
a prominent ridge, the crista galli of human
anatomy, extends nearly the entire length of the
fossa. The cribriform plate, forming the ante-
rior wall, is perforated by numerous foramina for
filaments of the olfactory nerve. These foramina
are larger and more numerous at the periphery of
the plate. In the lateral wall of the fossa is a
larger opening, the ethmoidal foramen.
The cerebral fossa, much the largest of the
cranial fossae, houses the cerebrum. As in the
bears, a vertical ridge (the site of the sylvian fissure
of the brain) separates a larger anterior fronto-
parietal region from a smaller posterior temporal-
occipital region. This ridge is less obvious in the
smaller arctoids. The walls of the fossa bear nu-
merous ridges and furrows that conform to the
gyri and sulci of the cerebral cortex of the brain.
A conspicuous groove immediately in front of the
sylvian ridge lodges the middle meningeal artery;
a smaller groove, which houses a branch of this ar-
tery, lies in the posterior region of the fossa (fig. 22).
In Ursus and other arctoids the groove for the
middle meningeal artery lies in the posterior re-
gion of the fossa.
The cerebellar fossa is largely separated from
the cerebral fossa by the tentorium osseum,
which forms most of its anterior wall. The ten-
torium is exceptionally well developed in the bears
and pandas. The cerebellar fossa communicates
with the cerebral fossa via the tentorial notch, a
large opening that in Ailuropoda is much higher
than wide; in f7rsMS it is more nearly square. The
tentorium slopes backward at an angle of only
about 10 in Ailuropoda, while in Ursus this angle
is about 25. The slope is much greater in other
arctoids (about 45).
The walls of the cerebellar fossa are grooved and
perforated by various venous sinuses (see p. 281) ;
otherwise they conform to the shape of the cere-
bellum. The medial face of the petrosal is visible
in the wall of this fossa. As in Ursus and Ailurus,
the tentorium is in contact with the petrosal along
the entire petrosal crest, and covers the part of the
petrosal anterior to this line. In Canis and the
procyonids, in which the tentorium is not so well
developed, an anterior face of the petrosal is also
exposed in the cerebral fossa. The enlarged ten-
torium in the bears and pandas has also crowded
out the trigeminal foramen the large opening in
the petrosal near the apex that is so conspicuous
in canids and procyonids. In the ursids the root
of the trigeminal nerve passes over, instead of
through, the apex to enter the trigeminal fossa.
In Ailuropoda the most conspicuous feature on the
medial face of the petrosal is the internal acous-
tic opening, leading into the internal acoustic
meatus. Immediately behind this opening is a
smaller foramen, the aquaeductus vestibuli,
overhung by a prominent scale of bone. Just
above and behind the acoustic opening is a bulge
in the surface of the petrosal, the eminentia ar-
cuata, caused by the superior semicircular canal.
In all other arctoids examined (except Procyon)
there is a deep pit, larger than the acoustic meatus
and situated directly above it, that houses the
petrosal lobule or "appendicular lobe" of the cere-
bellum; this pit is wanting in Ailuropoda and Pro-
cyon. The inferior border of the petrosal is grooved
for the inferior petrosal sinus, and the superior
angle is crossed by the groove for the transverse
sinus.
The floor of the cerebral and cerebellar fossae
exhibits several features of interest (fig. 22). The
dorsum sellae marks the boundary between the
cerebral and cerebellar spaces. Most anteriorly,
near the middle of the cerebral fossa, is the open-
ing for the optic nerve. It leads into a canal,
nearly 25 mm. long, that opens in the orbit as the
optic foramen. This canal is of comparable length
in Ursus but is short in other arctoids. Behind
the optic opening is a prominent sulcus for the
optic chiasma, of which the canal itself is a con-
tinuation. The sella turcica lies in the midline
at the posterior end of the cerebral fossa. Of the
components of the sella, the tuberculum sellae
is wanting anteriorly, but the anterior clinoid
processes at the anterior corners are well devel-
oped; these processes, to which the dura is attached,
are often wanting in arctoids. The posterior
clinoid processes are plate-like lateral extensions
of the dorsum sellae, overhanging the cavernous
sinuses laterally. These processes, to which the
dura also attaches, are well developed in all arc-
toids examined except Canis, where they are want-
ing. The hypophyseal fossa is a well-bounded
pit in all arctoids except Canis, in which there is
no anterior boundary.
58
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Impressio
A. meningea med.
For. ovale
Fossa trigem
Hiatus canalis facialis
For. carot.ant.
Siniis petrosus inf.
Meatus acusticus interims
Aquaedudus restibuli
For. lacerum post.
Sinus sigmoideiis
Can. hypoglossi (condyloideum)
For. mastoideum
Sinus transversus
For. opticum
Fissura orbitalis +
For. rotuiidum
Proc. clinoideus ant.
Sella turcica
Sinus carer nosus
T Dorsum sellae
Proc. clinoideus post.
Clirus
Pars basilaris occipitale
For. magnum
Fig. 22. Left half of basicranium of Ailuropoda, internal view.
On either side of the sella turcica is a wide longi-
tudinal sulcus, extending from the orbital fissure
anteriorly to the petrosal bone posteriori}', in
which the cavernous sinus Hes. Anteriorly the
sulcus opens into the orbit through the large open-
ing formed by the combined orbital fissure and
foramen rotundum; fusion of these two foramina
is peculiar to Ailuropoda. A ridge on the floor of
the sulcus marks the boundary between the orbital
fissure (medial) and foramen rotundum (lateral) of
other arctoids. In the posterior part of the sulcus,
just in front of the apex of the petrosal, is a deep
narrow niche, the trigeminal fossa, which lodges
the semilunar ganglion of the trigeminal nerve.
The foramen ovale (third and fourth branches of
trigeminus) opens into the floor of the niche an-
teriorly; in Ursus, in which the trigeminal fossa
extends farther anteriorly, both the foramen ro-
tundum (^second branch of trigeminus) and the
foramen ovale open directly into it. A small roimd
opening at the posterior end of the trigeminal fossa
is the outlet of the hiatus canalis facialis,
through which the great superficial and deep pe-
trosal nerves enter the cranial cavity. Imme-
diately above this is a smaller opening (more
conspicuous in Ursus), the foramen petrosum
superior, the anterior outlet of the superior pe-
trosal sinus.
The anterior carotid foramen Hes at the an-
terior corner of the petrosal, directed anteriorly
and medially. In Ailuropoda, in which there is
no foramen lacerum medium, the internal carotid
artery passes from the carotid canal directly into
the cavernous sinus, and the anterior carotid fora-
DAVIS: THE GIANT PANDA
59
men is thus intracranial. In Ursus, the artery,
after leaving the carotid canal, passes ventrad into
the foramen lacerum medium, where it immedi-
ately doubles back upon itself to pass nearly ver-
Sinus cavernosus'
Sinus petrosus iiif/
sinus runs nearly vertically, connecting the sagit-
tal sinus above with the vertebral vein below. It
is sharply divided into inferior and superior parts.
The inferior section, much larger in caliber, lies
Sinus sagillatis sup.
Sinus rectus
Sinus transversus (pars sup:)
Sinus temporalis
.V mastoidea
Sinus transversus (pars inf)
V verlebralis
Sinus sigmoideus
To V jugularis int.fvia for. lac. post J
To V facialis inl.[via for. postglenj
Sinus petrosus sup.
Fig. 23. Sinuses and diploic veins. Right half of skull of Ailuropoda, internal view (semi-diagrammatic).
tically into the cavernous sinus. Thus in Ursus
the foramen in the floor of the cavernous sinus is
the internal opening of the foramen lacerum me-
dium, and the anterior carotid foramen is visible
only externally within the foramen lacerum me-
dium. The situation in Ailurus and Procyon is
similar to that in Ursus. Obliteration of the fora-
men lacerum medium and of the associated flexure
in the internal carotid artery in Ailuropoda is un-
doubtedly correlated with the general crowding of
non-masticatory structures in this region and is
therefore without functional or taxonomic signifi-
cance. Cams, as usual, is quite different from either
the Ursidae or Procyonidae.
The inferior petrosal sinus lies just mesad of
the petrosal, largely roofed over by a lateral wing
of the clivus. The sinus is continuous anteriorly
with the cavernous sinus and posteriorly with the
sigmoid sinus, which name it assumes at the fora-
men lacerum posterior, at the posterior corner of
the petrosal. The superior petrosal sinus is re-
duced to thread-like caliber in Ailuropoda and
Ursus as a result of the great development of the
tentorium. It opens into the trigeminal fossa via
the superior petrosal foramen, at the apex of the
petrosal. From here the sinus arches posteriorly
around the petrosal, enclosed in the temporal bone,
and enters the temporal sinus. The transverse
in an open groove behind the petrosal, the upper
part of the groove crossing the petrosal. The
mastoid foramen and several diploic veins open
into this part of the sinus. At the dorsal border
of the petrosal the sinus gives off the large tem-
poral sinus, which descends as a closed canal to
open extracranially via the postglenoid foramen.
The superior section of the transverse sinus con-
tinues dorsad as a closed canal, much reduced in
caliber, to open into the sagittal sinus at the dorsal
midline. The sagittal sinus is visible for a vari-
able distance as a shallow groove along the midline
of the roof of the cerebral fossa. The short sig-
moid sinus runs posteriorly from the foramen
lacerum posterior, meeting the transverse sinus at
a right angle about 5 mm. behind the posterior bor-
der of the petrosal. Beyond the confluence of the
inferior petrosal and transverse sinuses a groove,
which houses the vertebral vein, continues caudad
through the lateral corner of the foramen magnum.
The vertebral vein lies in a similar groove in Ur-
sus, while in all other arctoids examined (including
Ailurus) the groove is roofed over to form a canal.
From the dorum sellae the floor of the basi-
cranium slopes backward and downward as the
clivus. This region is basin-shaped to conform
to the shape of the pons, and is separated by a
transverse ridge from the basilar portion of the
60
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
M. pterygoideus
ext
For. matidibularis
M. pterygoideus int.
M. temporalis (prof.)
Proc. morytnw
M. digastrii
M. temporalis superf.+
M. zygomaticomandibularis
Fossa masseterica
Proc. angutaris
^_ _ ^, M. masseter
For. merUaiia
Fig. 24. Left mandible of Ailuropoda: external surface lower right, internal surface upper left.
basioccipital bone lying behind it, which supports
the medulla. The whole plate-like floor of the
basicranium lying behind the dorsum sellae is
shorter and wider in Ailuropoda than in Ursus.
The hypoglossal (condyloid) foramen pierces
the floor of the basilar portion in a lateral and
slightly anterior direction, just anterior to the
foramen magnum.
Mandible. The mandible of Ailuropoda is no-
table for its extreme density. Its weight is more
than twice that of the mandible of a much larger
bear. The two halves of the mandible are firmly
fused at the symphysis, with no trace of a suture,
in all adults examined. This is contrary to the
condition in Ursus and other arctoids. Fusion
is nearly complete in a young adult Ailuropoda,
in which most skull sutures are still open. The
length of the symphysis is also remarkable. It is
relatively nearly twice as long as in Ursus, and
extends to the anterior border of the first molar
instead of the third premolar. In Ailurus, by
contrast, the symphysis is short (barely reaching
the first premolar), and the two halves of the man-
dible do not fuse.
The body of the mandible, viewed from the
side, tapers from the ramus forward, whereas in
Ursus (but not in other arctoids) the height of the
body is quite uniform. Among several mandibles
of Ailuropoda the inferior border is curved in vary-
ing degrees, reaching its nadir below the second
molar; in one mandible this border is nearly as
straight as in Ursus. The body is less high ante-
riorly than in Ursus, and higher posteriorly, and
this is probably correlated with the relatively feebly
developed canines and the large molars. The up-
per or alveolar border of the body lies about 30 mm.
below the level of the articular condyle, whereas
in Ursus these are at very nearly the same level
(fig. 25). There are typically two mental fora-
mina, as in arctoids in general. These are sub-
equal in size. The more anterior foramen is often
broken up into several smaller foramina.
Throughout its length the body is more than
twice as thick as in Ursus, and viewed from below
the body arches abruptly laterad at the posterior
end of the symphysis, giving a Y-shape to the ven-
tral outline of the jaw.
DAVIS: THE GIANT PANDA
61
Ailuropoda 31128. Basal skull length 235 mm.
Ursus 21859. Basel skull length 303 mm.
Fig. 25. Outlines of posterior ends of mandible of Ailuropoda (solid line) and Ursus horribilis (broken line) superimposed.
Note (1) the excavation of the posterior border of the coronoid process, (2) the much deeper masseteric fossa, and (3) the
depressed occlusal plane in Ailuropoda.
The ramus, which is that part of the mandible
lying posterolaterad of the last molar, differs from
that of Ursus in several important respects. Be-
sides bearing the mandibular condyle, the ramus
functions chiefly for the insertion of the muscles
of mastication. The areas where these muscles
attach are large, well marked, and rugose in
Ailuropoda.
The masseteric fossa, in which the zygomatico-
mandibular muscle inserts, is larger than in Ursus
in both vertical and transverse diameters. The
vertical diameter in particular has been increased
relative to Ursus (and other arctoids) by exten-
sion ventrad. It is also deeper, for the edges have
been built out. The surface of the fossa is ex-
tremely rugose, and is marked by several promi-
nent transverse ridges (cristae massetericae) for
the attachment of tendinous sheets in the muscle.
The coronoid process, into which the masseteric
fossa grades imperceptibly, functions in the in-
sertion of the temporal muscle on both its lateral
and medial surfaces. This process is similar to
that of Ursus, except that its posterior border is
eroded away, giving it a scimitar-like form and
greatly reducing the area available for temporal
insertion (fig. 25) . The angular process is a small
but conspicuous prominence on the posteromedial
border of the ramus, below the condyle. It pro-
jects medially and posteriorly, instead of posteri-
orly as in other arctoids. This process characteris-
tically provides insertion for part of the masseter
on its outer surface and part of the internal ptery-
goid on its inner surface; none of the masseter
fibers reach it in Ailuropoda. In Ursus and other
arctoids (including Ailuru^) the angular process is
large and tongue-like, with well-marked muscle
scars for both the masseter and the internal ptery-
goid. In Ursus a conspicuous marginal process
(Toldt's terminology) on the inferior border of the
ramus, anterior to the angular process, provides
the main insertion for the digastric muscle. This
process is wanting in other arctoids. In Ailuro-
poda the insertion of the digastric is more diffuse
than in Ursus, and the marginal process, while
present, is less clearly marked and is situated on
the medial surface of the mandible immediately
in front of the internal pterygoid scar.
Hypertrophy of the jaw-closing muscles in the
giant panda is reflected in the relatively larger
areas of attachment on the skull. The total area
of insertion of the masseter and temporal on the
lateral surface of the mandible was calculated
roughly by plotting on millimeter paper. In Ailu-
ropoda (basal skull length 252 mm.) this area
amounted to 5368 mm.-, while in a much larger
62
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
LACRIMALE
ORBITOSPHENO/D
PTERYGOID
Fig. 26. Lateral view of juvenile skull of Ailuropoda (USNM 259076), showing sutures.
Ursus horribilis (basal skull length 303 mm.) it
was only 4774 mm.-
The medial surface of the ramus exhibits con-
spicuous scars marking the attachment of several
muscles. A rugose area occupying most of the
medial surface of the coronoid process marks the
insertion of the deep layer of the temporal muscle.
The anterior border of this area sweeps back be-
hind the last molar, leaving a triangular space
(about one-fourth of the total medial coronoid
surface) free of muscle attachment. The ventral
border of the temporal area is a prominent hori-
zontal crest at the level of the alveolar border,
extending back immediately above the mandibular
foramen; this is the level to which the temporal
insertion extends in other arctoids. Immediately
behind this crest, on the dorsal surface of the con-
dyle, is the extraordinarily conspicuous, pock-like
pterygoid depression that marks the insertion
of the external pterygoid muscle. A much larger
scar, below the condyle and extending back onto
the angular process, marks the insertion of the in-
ternal pterygoid. A triangular rugose area in front
of this, beginning posteriorly at the marginal proc-
ess, marks the insertion of the digastric. The
mandibular foramen, for the inferior alveolar
vessels and nerve, is circular instead of oval in
cross section. It lies immediately above the mar-
ginal process.
The condyloid process has the transverse semi-
cylindrical form characteristic of the Carnivora,
but in Ailuropoda this region is an exaggeration
of the usual arctoid condition. The neck support-
ing the capitulum is short, flattened, and twisted
through 90 the typical carnivore arrangement.
As a result, the medial half of the capitulum is
buttressed anteriorly but unsupported below, while
the lateral half is buttressed below but unsup-
ported anteriorly. In all arctoids the articular sur-
face tends to conform to this support pattern, the
medial half facing posteriorly and the lateral half
more or less dorsally. In Ailuropoda this tendency
reaches full expression, and the articular surface is
a spiral track rotated through more than 90, "like
a riband wound obliquely on a cylinder," as Lydek-
ker stated. To some extent at least, this spiral
form is correlated with the large size and dorsal
position of the pterygoid depression, which in Ailu-
ropoda occupies a part of the area of the articular
surface of other carnivores.
The width of the capitulum much exceeds that
of any other carnivore. The index basal skull
length /width capitulum is .27 to .31 for Ailuropoda,
while for Ursus it is only .15 to .17. Ailurus is
intermediate, with an index of .22 to .23, while
all other carnivores examined were below .18 ex-
cept an old male zoo specimen of Tremarctos or-
natus, in which it was .21. The long axis of the
capitulum is oriented at nearly a right angle to
the axis of the skull in both horizontal and verti-
cal planes. As in carnivores in general, however,
the medial end of the axis is tilted slightly caudad
and ventrad of 90.
B. Cranial Sutures and Bones of the Skull
As was mentioned above, the sutures disappear
early in Ailuropoda, and nearly all are completely
obliterated on fully adult skulls. The following
account of the bones of the skull is based on a
young female skull, with a basal length of 213 mm..
DAVIS: THE GIANT PANDA
63
PREMAXI LLA
PER I OTIC
CPars mastoidta)
^<//>
occ\P^^
Fig. 27. Ventral view of juvenile skull of Ailuropoda (USNM 259076), showing sutures.
on which all but a few of the sutures are still open
(figs. 26, 27). This skull is intact, so that only
surface features could be examined.
For the most part, the relations of the bones
differ so little from those of Ursus that there is
no point in a detailed description. The exact po-
sitions of the sutures are shown in the accompany-
ing drawings.
The premaxilla is essentially similar to that of
Ursus.
The maxilla is modified to accommodate the
enlarged cheek teeth. The posterior part of the
bone forms an enormous maxillary tuberosity that
supports the second molar. The tuberosity carries
the maxilla back to the level of the optic foramen,
whereas in Ursus it extends only to the pterygo-
palatine foramen. In the juvenile skull this pos-
terior extension of the maxilla has a remarkably
plastic appearance, as if the bone had flowed back
over the vertical plate of the palatine, squeezing
the pterygopalatine and sphenopalatine foramina
upward against the inferior orbital crest. A sec-
tion through this region (fig. 21) shows that the
maxilla lies outside the palatine that the latter
is not displaced backward.
64
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
As in Ursus, at the anteromedial corner of the
orbit the maxilla is wedged in between the lacri-
mal and jugal, forming a part of the anterior, all
the lateral, and a part of the medial boundaries
of the lacrimal fossa.
The anterior zygomatic root contains a lateral
extension of the maxillary sinus, not seen in any
other carnivore.
The nasals, as in Ursus, are short and their
lateral borders are not prolonged forward as in
other arctoids.
The lacrimal closely resembles the correspond-
ing bone in Ursus, which Gregory characterized
as "much reduced, sometimes almost vestigial."
It is a minute plate, about 5 mm. wide and 12 mm.
high, withdrawn entirely from the anterior rim of
the orbit, and forming only a small part of the
medial surface of the lacrimal fossa. The lacrimal
of Ailurus is essentially similar. It is slightly
better developed in the procyonids.
The jugal (malar) does not depart in any essen-
tial respect from the typical arctoid pattern.
The palatine, except for the superficial modi-
fication produced by the posterior prolongation of
the maxilla over the pars perpendicularis, is sim-
ilar to that of other arctoids. The pars horizontalis
extends forward on the palate slightly anterior to
the first molar.
The vomer differs from that of Ursus and most
other arctoids in the great posterior extent of its
pars sagittalis. Otherwise its relations are similar
to those of Ursus.
The frontal, parietal, squamosal, and oc-
cipital have all suffered more or less change in
form with the remodeling of the skull to accom-
modate the enormous masticatory musculature.
Except for the morphologically insignificant dif-
ferences resulting from this remodeling, the rela-
tions of these bones are typical.
The frontoparietal suture, which is relatively
straight and about at a right angle to the axis of
the skull in Ursus and other arctoids, here arches
forward to the level of the optic foramen. At the
dorsal midline a narrow tongue of the frontal pro-
jects posteriorly between the parietals for about
15 mm., i.e., to about the level of the whole fronto-
parietal suture in Ursus. This suggests that in
Ailuropoda the parietal has increased anteriorly
at the expense of the frontal.
The interparietal suture is obliterated, and a
secondary upgrowth of bone is approaching the
site of the future sagittal crest.
On the skull examined, the basioccipital-supra-
occipital suture was still open, but the exoccipital-
supraoccipital suture was closed.
The mastoid portion of the periotic is exposed,
as is usual in arctoids, on the posterior side of the
mastoid process, where it is wedged in between
the squamosal and the occipital. The suture be-
tween the periotic and the tympanic disappears
early in all arctoids, and was gone in the skull of
Ailuropoda studied.
The tympanic, in so far as it is visible exter-
nally, differs considerably in shape from the cor-
responding bone in Ursus. It is obvious, however,
that this bone has merely been crowded by the
surrounding structures, particularly the postglenoid
process. The relations of the tympanic are almost
exactly as in Ursus, and posterior expansion of the
postglenoid process as seen in Ailuropoda might
be expected to alter the form of the tympanic pre-
cisely as it has. (This region is described in detail
on p. 319).
The sphenoidal complex has been affected rela-
tively little by the remodeling of the skull and is
very similar to the corresponding region in Ursus.
In the skull examined, the four elements constitut-
ing the complex (basisphenoid, presphenoid,
alisphenoid, orbitosphenoid) are still distinct.
They differ only in the most trivial respects from
the corresponding elements in a young Ursus skull.
The pterygoid is completely fused with the
sphenoid, and this is one of the very few sutures
of the skull that have been obliterated at this age.
This condition contrasts sharply with Ursus at a
comparable age, in which the pterygoid is still en-
tirely separate.
The ethmoid is not visible on the surface of
the skull.
The following sutures are closed in the young
skull examined: tympanic-periotic, exoccipital-
supraoccipital, pterygoid sphenoid, interparietal.
The first two fusions are characteristic of carni-
vores at this stage of development. The last two
are not, and represent departures from the car-
nivore pattern.
C. Hyoid
The hyoid (fig. 28) differs little from that of
bears and other arctoid carnivores. It is composed
of the usual nine rodlike bony elements, suspended
from the basicranium by a pair of cartilaginous
elements, the thyrohyals. The hyoid fossa, at the
bottom of which the thyrohyal articulates with
the skull, lies in the hyojugular fossa.
The hyoid consists of a transverse body and two
horns (cornua), an anterior composed of three pairs
of bones plus the cartilaginous thyrohyals, and a
posterior composed of a single pair of bones.
Like all other bones of the skeleton, the hyoid
bones of Ailuropoda exhibit more pronounced scars
DAVIS: THE GIANT PANDA
65
Slylohyal
Cornu
anterior
Epihyal
Cornu anterior
Cornu posterior
Thyrohyal
Cornu posterior
Corpus
Ceratohyal
Fig. 28. Hyoid of Ailuropoda, lateral and ventral views.
for muscle attachments than they do in Ursus,
although the bones themselves are no more robust.
In both the giant panda and the bears the body is
a transverse rod, less plate-like than in other arc-
toids. The ceratohyal is also less expanded than in
other arctoids, and in Ailuropoda it has a distinct
longitudinal furrow on the dorsal surface. The
epihyal presents nothing noteworthy. The stylo-
hyal is flattened and plate-like, with an irregular
outline, in Ailuropoda. The thyrohyal is slightly
curved and rodlike.
D. Review of the Skull
The skull and teeth of Ailuropoda were described
in some detail by A. Milne-Edwards (1868-1874),
Lydekker (1901), Bardenfleth (1913) and Gregory
(1936). Each of these made point by point com-
parisons with the Ursidae on the one hand and
with Ailurus and the Procyonidae on the other,
in an attempt to determine the affinities of Ailur-
opoda. Conclusions were conflicting; the only
legitimate conclusion is that the skull and denti-
tion of the giant panda are so modified that the
affinities of this animal cannot be determined from
these structures alone. I have therefore used
other characters in deciding the affinities of Ailur-
opoda, which are unquestionably with the Ursi-
dae. Here the only important consideration is
that no skull or dental character shall point un-
equivocally to relationship with any other group
of carnivores.
The demands of the masticatory apparatus in
Ailuropoda have resulted in such extensive and
permeating modifications in the skull that many
elements have been modified beyond the limits of
inter-generic or even inter-family differences with-
in the Carnivora. Among those not so affected
are the pattern (but not the extent) of the para-
nasal sinuses, the turbinates, and the middle ear
all intimately associated with primary sense
organs and not affected by muscle action. Each
of these structures is very similar to the correspond-
ing structure in Ursus. Klatt (1912) has shown
that the extent of the frontal sinus is determined
by the mass of the temporal muscle, as would be
expected, because the sinus lies between the outer
and inner lamina of the cranium. The temporal
attaches to the outer lamina, whereas the inner
lamina encapsulates the brain.
Aside from its function of encapsulating the
brain and sense organs, the generalized carnivore
skull is designed primarily for seizing and cutting
up prey. Skulls of omnivorous or herbivorous
carnivores are secondary modifications of this pri-
mary predatory type. Consider the skull of a
generalized carnivore, such as Canis or Viverra, as
a construction. How does such a construction
compare with those of other generalized mammals
in architecturally or mechanically significant ways?
1. The skull is elongate and relatively slender
(see Table 8). Elongation of the head is a primi-
tive mammalian feature that has been retained in
66
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Table 8. SKULL PROPORTIONS IN GENERALIZED AND SPECIALIZED CARNIVORES
N =
SKULL LENGTH:
Condylobasal length
Length thor. vert. 10-12'
FACE LENGTH:
Gnathion-ant. end braincase
Condylobasal length
Preoptic length
Condylobasal length
SKULL DEPTH:
Vertex-inf . border mandible
Condylobasal length
SKULL BREADTH:
Zygomatic breadth
Condylobasal length
Least diam. braincase
Condylobasal length
See page 35.
Generalized Flesh-
eating Carnivores
Canis Viverra
lupus tangalunga
Predominantly
Herbivorous
Carnivores
Procyon Ailurus
lotor fulgens
Ursus
Extremely Powerful
Jawed Carnivores
Ailuropoda Hyaena
3
5
3
3
5
3
4
3.2
2.9
3.1
2.9
3.2
2.7
3.5
(3.08-3.23)
(2.75-2.95)
(3.04-3.24)
(2.53-3.21)
(2.99-3.44)
(2.63-2.72)
51
42
38
36
50
49
49
(50-51)
(40-43)
(37-39)
(34-38)
(46-52)
(47-53)
(48-50)
45
33
30
23
33
31
32
(42.1-46.6)
(31.8-33.6)
(29.1-30.1)
(22.4-24.1)
(31.4-35.5)
(29.2-32.0)
(30.5-33)
49
43
59
68
52
71
71
(48-51)
(40-47)
(56-62)
(67-69)
(47-57)
(70-72)
57
50
68
75
63
82
71
(55-60)
(49-52)
(65-70)
(71-79)
(57-69)
(81-82)
(66.5-75)
18
15
21
22
24
18
18
(17-19)
(14-16)
(20-22)
(22-23)
(22-26)
(15-20)
(16-20)
the Carnivora; the skull was elongate in the creo-
dont ancestors of the carnivores and is characteris-
tic of generalized mammals.
As a tool for seizing and cutting up prey an
elongate skull (particularly an elongate face) has
certain inherent mechanical advantages and dis-
advantages. Speed of jaw closure at the level of
the canines is achieved, though at the cost of
power. But production of useful force at the sec-
torial teeth is mechanically very unfavorable, since
more than twice as much disadvantageous force
is developed at the mandibular articulation (see
p. 69).
Preoptic length is a useful measure of face length
for our purpose, since it approximately divides the
tooth-bearing anterior part of the skull from the
posterior muscle-attachment part. Calculated in
this way, the face is long in Canis, moderately long
in Viverra. Both fall within the known range of
the Paleocene Arctocyonidae, the oldest and most
primitive of all carnivores: Deltatherium 31 per
cent, Eoconodon 38 per cent, Loxolophodon 45 per
cent.'
Depth and breadth of skull, both intimately as-
sociated with mechanics of the jaw, are moderate
in both Canis and Viverra. The civet is more
slender in both dimensions.
2. Two areas dominate the dental battery: the
enlarged dagger-like canines anteriorly, and the en-
> Calculated from illustrations in Matthew (1937).
larged scissor-like carnassials (P^ and MO poste-
riorly. The remainder of the dentition is more or
less degenerate. These two specialized areas of
the dentition are the key adaptation of the Car-
nivora. All other modifications of the skull away
from the generalized mammalian condition are
effectors of these seizing and cutting tools. These
modifications are as follows:
3. The mandibular articulation is a transverse
cylinder rotating in a trough-like fossa that is
strongly buttressed above and behind. This ar-
rangement permits only a hinge movement of the
mandible, plus limited lateral shifting of the man-
dible; the two may be (and probably normally
are) combined in a spiral screw movement. The
two halves of the mandible are not fused at the
symphysis, which indicates that they are capable
of at least some independent movement.
4. The mandibular articulation is at the level
of the occlusal plane, and therefore upper and
lower toothrows operate against each other like
the blades of a pair of shears.
5. The canines interlock and act as a guide for
the anterior part of the mandible as the jaws ap-
proach closure (and the carnassials begin to func-
tion). This is very evident from the wear areas
on the canines. The interlocking restricts lateral
movement and guides the two blades of the shear
very precisely past each other. Xo such arrange-
ment exists in such generalized marsupials as the
opossum or in generalized insectivores.
DAVIS: THE GIANT PANDA
67
^\ Z i 4 5 67 89 (0
Ailuropoda
Fig. 29. Differences of skull proportions in Ursus horribilis and Ailuropoda melanoleuca shown by deformed coordinates.
6. The temporal fossa is large, providing space,
and particularly attachment surface, for the large
temporal muscle (see p. 150). This fossa is simi-
larly large in generalized primitive mammals. The
masseteric fossa does not differ significantly from
that of primitive mammals. The pterygoid fossa
is small or wanting. This fossa is well developed
in primitive mammals; its reduction in the Carni-
vora is associated with the reduced size and im-
portance of the pterygoid muscles.
7. The zygomatic arch is strong and forms a
smooth uninterrupted curve in both the sagittal
and frontal planes. The anterior buttress of this
arch system lies directly over the primary cheek
teeth, the posterior buttress over the mandibular
fossa the two sites where pressure is applied dur-
ing mastication. The zygomatic arch represents
the "main zygomatic trajectory" of Starck (1935) ;
it is the principal structure within which are re-
solved the disintegrating forces generated by the
powerful jaw muscles. The arch is well constructed
and extremely powerful in Didelphis. In general-
ized insectivores, by contrast, the arch is structur-
ally weak: the curvature is interrupted (Erina-
ceus), parts of the arch are almost threadlike
{Echinosorex, Talpidae), or the central part of
the arch is missing (Soricidae).
Support for the canines, by contrast, is relatively
weak in generalized Carnivora. The main element
of this support system is the "vertex trajectory,"
which in generalized carnivores is weak and often
interrupted at the glabella.
What, now, has happened to this basic carnivore
construction in herbivorous carnivores, and par-
ticularly in the purely herbivorous giant panda?
The skull is still elongate, but slightly less so
than in Canis or Viverra (Table 8). In Ursus the
skull is even slightly longer than in Canis or Vi-
verra. There is, in fact, little variation in relative
skull length among all arctoids examined.
Face length in the giant panda is only slightly
less than in Viverra, and in the bears it is prac-
tically identical with Viverra. Proportions vary
among other herbivorous carnivores: the face is
very short in Ailurus, of normal length in Procyon.
Face length is extremely variable among the Car-
nivora in general, and the significance of this vari-
ability has not been explored. The face varies
independently of the cranium in mammals (p. 72).
We may conclude that Ailuropoda and Ursus show
no significant differences from the generalized carni-
vore condition in longitudinal proportions of the skull.
68
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Ailuropoda
Fig. 30. Difference.s of skull proportions in Canis lupus and Ailuropoda melanoleuca shown by deformed coordinates.
Depth and breadth of skull, on the contrary, in
all herbivorous carnivores depart significantly from
the generalized condition (see figs. 29 and 30, and
Table 8). Among these, depth is least in Ursus,
in which it scarcely exceeds that of the wolf.
Depth of skull in Ailuropoda is equaled among
carnivores only in Hyaena; in both the panda and
the hyena, depth is achieved largely by develop-
ment of a high sagittal crest, the inner lamina of
the skull roof remaining unaffected. The skull is
typically deep in all arctoids that have forsaken a
purely carnivorous diet. Increase in depth in-
volves only the external lamina of the cranium
and adjoining parts of the mandible not the face
or the direct housing of the brain. The vertical
height of the posterior half of the zygomatic arch,
the area from which the zygomaticomandibularis
takes origin, is also greatly increased in Ailuropoda.
DAVIS: THE GIANT PANDA
69
Zygomatic breadth is consistently greater than
in generalized flesh-eaters, and once again this
is maximal in Ailuropoda and least in Ursus.
Breadth in the powerful-jawed Hyaena is equal
to that in most herbivorous carnivores, but is con-
siderably less than in Ailuropoda.
We may conclude that breadth and depth of skull
are increased in all herbivorous carnivores, and that
these reach a maximum in Ailuropoda.
Increased breadth and depth of the cranium
produce increased volume of the temporal fossa.
In Ailuropoda the volume of this fossa has been
further increased, especially anteriorly, by crowd-
ing the orbit downward from its normal position,
by carrying the temporal fossa anteriorly at the
expense of the postorbital process and the poste-
rior part of the frontal table, and by decreasing
the anterior breadth of the braincase. The vol-
ume of this fossa probably approaches the maxi-
mum that is compatible with normal functioning
of surrounding structures.
Besides providing space for a greater volume of
craniomandibular musculature, increased depth of
skull greatly improves efficiency for production
of pressure at the level of the cheek teeth. Worth-
mann (1922) uses a simplified system of vector
analysis to compare relative masticatory efficiency
in man and several carnivores. He represents the
action of the masseter and temporal muscles by
straight lines connecting the midpoints of origin
and insertion areas. The axis of the masticatory
system is represented by a straight line connecting
the center of rotation of the mandibular articula-
tion with the last molar tooth.
From the structural standpoint, greater depth
of skull increases the magnitude of vertical forces
that the skull is capable of withstanding.
Comparison of masticatory efficiency in a gen-
eralized carnivore iCanis) and in the purely her-
bivorous Ailuropoda by Worthmann's method re-
veals a striking improvement in the panda (fig. 31).
In the wolf the axis of the masseter (m) intersects
the masticatory axis GK at a point about 30 per
cent of the distance from G to K. Thus force at
the joint (G) would be to force at the cheek teeth
(K) as 7 : 3; in other words joint force is about
2.5 times as great as useful chewing force. In the
panda, by contrast, k : fir = 55 : 45 approximately.
Similarly for the temporalis k:g = 28:12 for
Canis, whereas k : g = 47 : 53 for Ailuropoda.
In the cheek-tooth battery emphasis has shifted
from the sectorial teeth to the molars (p. 128), and
the anterior buttress of the zygomatic arch now
lies over the first (Ailuropoda) or second (Ursus)
upper molar. This shift, by shortening the resist-
ance arm of the jaw lever, increases the mechanical
efficiency of the system for production of pressure.
The form of the mandibular articulation has not
changed it is still a transverse cylinder rotating in
a trough. The extensive horizontal movements of
upper molars against lower that characterize other
herbivorous mammals are therefore limited to a
slight lateral displacement in herbivorous carni-
vores. Because of the interlocking canines at the
anterior end of the system, no lateral shifting is
possible with the teeth in full occlusion.'
In Ursus the mandibular articulation is at the
level of the occlusal plane as in generalized flesh-
eating carnivores. In Ailuropoda the articulation
lies considerably above the occlusal plane. Lebe-
dinsky (1938) demonstrated that elevating the
articulation above the occlusal plane imparts an
anteroposterior grinding movement at the occlusal
plane, even when the mandible is swinging around
a fixed transverse axis.
Lebedinsky's interpretation may be analyzed
further. Figure 32, A, represents a mandible with
the mandibular articulation (0) at the level of the
toothrow. A point x on the lower dentition travels
through the arc x~x' when the mouth is opened.
The tangent to this arc at point x is perpendicular
to the occlusal plane, and therefore there is no
anteroposterior component in the movement of x
with respect to the axis AO, and an object placed
between the upper and lower dentitions would be
crushed or sheared. This would likewise be true
at any other point on the axis AO.
Figure 32, B, represents a mandible with the
mandibular articulation (0) elevated above the
level of the toothrow. A point x travels through
the arc x-x' when the mouth is opened, but in
this case the tangent to the arc at x forms an acute
angle with the occlusal plane, A-B, and there is a
very definite anteroposterior component in the
movement of x with respect to the axis AB. The
angles formed by successive tangents along AB
become increasingly acute as B is approached,
until at B there is no longer any vertical compo-
nent at all. Thus, as Lebedinsky pointed out, any
object placed between the upper and lower denti-
tions would be subjected to anteroposterior forces
even with pure hinge movement of the jaw. More-
over, the anteroposterior force becomes increas-
ingly great as a point (B) directly beneath the
articulation is approached. In Ailuropoda, there-
fore, an anteroposterior grinding action is achieved
by elevating the articulation, and its effectiveness
is increased by extending the toothrow posteriorly.
' In Ailurus fulgens a lateroventral shifting of more than
2 mm., with the cheek teeth in complete occltision, is possible.
This is true grinding, otherwise unknown in the Carnivora.
Canis
Ailuropoda
Fig. 31. Relative masticatory efficiency in a generalized carnivore (Canis) and the giant panda (Ailuropoda). The line
KG, representing the masticatory axis, connects the center of rotation of the mandibular joint (G) with the midpoint of the
functional cheektooth area (K) (boundary between P' and Mi in Canis, anterior quarter of M' in Ailuropoda). The line m
represents the axis of the masseter. The line /, the axis of the temporalis, connects the approximate center of origin (T) of the
temporalis with the approximate center of insertion (C). The line / may be projected beyond C to K, since a force acting on
an immovable system may be displaced in its own direction without altering the result. True masticatory force is represented
by k, articular pressure by g.
70
DAVIS: THE GIANT PANDA
71
/
/
/
;
/
/
/
I
X
a
W
1
1
/
I
\ /
\
\ /
(
/
Fig. 32. Occlusal relations in a mandible with mandibular articulation at level of toothrow (A), and elevated above level
of toothrow (B). The lines AO and ABO represent the mandible in occlusion, A'O and A'B'O its position when the mouth
is opened. The points x and x' represent the positions of a cusp on one of the lower cheekteeth. (C) Occlusal relations in
AUuropoda in biting down at point x on an object 25 mm. in diameter (see text).
Stocker (1957) has calculated for the elephant
the anteroposterior displacement of a point on the
occlusal surface of a lower molar when the jaw is
lowered. A similar calculation may be made on a
panda skull (fig. 32, C). A point x at the anterior
end of the iirst lower molar is 125 mm. from the
center of rotation of the mandible, 0. The line xO
was found to form an angle, X, of 7 with the oc-
clusal plane, x B. The panda is known to chew
up bamboo stalks up to 38 mm. in diameter (p. 20) ;
to be conservative let us assume a bamboo stalk
25 mm. in diameter.
An object 25 mm. in diameter placed between
the upper and lower teeth at the level x displaces
point X on the lower molar to position x'. The
two lines x and x' form an angle, a, of 11 30'.
The horizontal displacement, j M, of x with re-
spect to the occlusal plane may be calculated as
a;M=a:OcosX-a:Ocos (X-|-a)
= xO [cos X -cos (X-|-a)]
Substituting the values given above, this equation
gives a value for x M of 5.4 mm., which is the
horizontal distance through which a point x on
the lower molar travels as the teeth are brought
into occlusion. This represents the anteroposte-
rior grinding component that would be brought
to bear on the bamboo stalk.
72
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
The mandibular symphysis remains unfused in
Ursiis and othei- herbivoi'ous carnivores, although
the two halves interlock so intimately that no
movement is possible. Its fusion in Atluropoda
reflects the general increase in bone tissue that
characterizes the skull as a whole.
We may conclude that the skull of Ailuropoda
represents an attempt to adapt the carnivore type
of skull already highly adapted for seizing and
cutting to the radically different requirements of
grinding siliceous plant fibers. Efficient grinding
requires horizontal movements, but these are al-
most completely inhibited by the cylindrical man-
dibular articulation and the interlocking of teeth
during occlusion, although Ailurus shows that
effective horizontal grinding can be achieved in a
carnivore. A compromise solution was to replace
the unattainable mechanical efficiency seen in true
herbivores with more power. This attempt to
achieve maximal power in the masticatory equip-
ment is the key to the architecture of the panda
skull.
The skulls of other more or less herbivorous car-
nivores except Ailurus exhibit most of the modi-
fications seen in Ailuropoda, but to a much less
extreme degree. Thus the skull of Ailuropoda may
be considered an ultimate expression of adaptation
for herbivory within the Carnivora.
What can be deduced of the morphogenetic
mechanisms whereby these results were achieved
in other words, the mechanism through which
natural selection had to operate? To what extent
does the skull of Ailuropoda as compared with that
of Ursus merely reflect extrinsic mechanical fac-
tors arising from the massive musculature, and to
what extent intrinsic factors, other than the ability
of the bone to respond to mechanical stress?
Some anatomists have recently attempted to re-
examine the mammalian skull from an analytical
rather than a purely descriptive standpoint (see
Biegert, 1957, for a review). In these studies the
skull is regarded as merely the bony framewoi-k
of a major functional unit, the head. During on-
togeny and phylogeny there is a complex interplay
among the various organs making up the head,
and the skull adapts itself to the changing spatial,
mechanical, and static demands. In a given phylo-
genetic sequence one of the head organs (e.g.,
brain, feeding apparatus, eyes) typically comes to
dominate the whole and sets the pattern, so to
speak, for further evolution within the group.
Changes in the skull are thus not simply additive,
but are a function of changes in other head organs,
which in turn may be functionally irreversible and
therefore in effect "fix" the pattern of further evo-
lution within the group. The causal factors that
determine changes in skull form are interpreted as
an interplay between the inherited basic plan of
the skull and the demands of other head structures
extrinsic to the skull itself. This approach iso-
lates some of the forces modeling the skull, but
in the end it does little more than describe struc-
tural correlations. It fails to come to grips with
the problem of the mechanics of evolution.
Correlation studies have shown that the facial
part of the skull varies as if it were genetically
distinct from the cranium, as it is in fact phylo-
genetically (Cobb, 1943; and especially Starck,
1953, for a review). This genetic independence,
and the further independence of the mandible,
have been proved in breeding experiments on dogs
(Stockard, 1941 ; Klatt, 1941^3) . Such independ-
ence means that a genetic factor affecting the
ontogenetic growth rate of the cranium (or a com-
ponent of the cranium) need not affect the face,
and vice versa. The union between face and cra-
nium, however disparate these structures may be,
is maintained by mutual accommodation during
growth. Genetic control of growth rates in dental
fields is well known to be distinct from that of any
other part of the skull. Numerous observations
(e.g., Cobb, 1943) indicate that the alveolar areas
of the skull accommodate directly to the space re-
quirements of the teeth during the gi-owth process.
The mammalian skull, in short, is a mosaic of
independent morphogenetic units that are fitted
into a functional unit partly by natural selection
acting on their several time-tables of gi'owth and
differentiation, and partly by accommodation to
extrinsic forces. The extent of the morphogenetic
units may vary with time during ontogeny: the
earlier in ontogeny a genetic effect is manifested,
the more extensive its target is likely to be. A
beginning has been made at identifying and iso-
lating these morphogenetic units (Starck, 1953;
Landauer, 1962), but they are still inadequately
known.
Thus, in considering the morphosis of the skull,
two sets of factors must be kept in mind. These
are the location and extent at any moment during
ontogeny of the morphogenetic units of which the
skull is composed (intrinsic to the skull), and the
modeling effects on the skull of other head struc-
tures (extrinsic to the skull as such).
In the skull of Ailuropoda the increase in quan-
tity of compacta is clearly limited to two major
morphogenetic units, the cranium and the man-
dible, and absent in a third, the face. The hyper-
trophy of bone substance affects not only the skull,
but all compacta in the body in a gradient falling
off from the dorsal body axis, and including struc-
tures such as the tail and the proximal ends of the
DAVIS: THE GIANT PANDA
73
ribs where hypertrophy can scarcely represent
structural adaptation. We do not know the time-
table of mammalian ontogeny in enough detail to
know whether these effects could have been pre-
dicted and delimited a priori. The additional bone
substance certainly strengthens the skull, although
it is not distributed along trajectory lines of the
skull as it should be if it were primarily functional.
We cannot say whether increased bone substance
in the skull of Ailuropoda was a primary target of
natural selection, whether it is genetically linked
with increase in the mass of the masticatory mus-
cles, or whether it simply reflects disturbed meta-
bolic or endocrine relations.
Cephalization in bulldogs is in some respects
similar to but less extreme than in Ailuropoda.
Klatt and Oboussier (1951) found that all struc-
tures of the head (skull, masticatory musculature,
brain, eyeballs, hypophysis) are heavier in bull-
dogs than in "normal" dogs. These authors con-
clude that the bulldog condition results from an
increase in the growth rate of the anterior end of
the embryo. More likely it represents a temporary
intensification of the general growth rate of the
embryo during the period when the head region
is undergoing its most rapid growth. The effects
are less generalized in Ailuropoda; here the brain
and eyeballs (and the internal ear) are of "nor-
mal" size, a condition that would result if the
ontogenetic growth rate were increased after the
central nervous system and its sensory adnexa had
experienced their period of most rapid growth.
The condition in the panda is, in fact, the reverse
of the condition in man, where the brain is en-
larged while all other cranial (but not facial)
structures are of "normal" size. As interpreted
by Weidenreich (1941), in man the ontogenetic
growth rate is temporarily intensified during the
period when the brain is undergoing its most rapid
growth, and returns to normal before the rapid
growth period of other cranial structures is reached.
It is known from comparative studies that sur-
face relief of the mammalian cranium is deter-
mined chiefly by the craniomandibular muscles
(Weidenreich, 1922). The developing cranium is,
as Anthony (1903) put it, molded between the
brain and the masticatory musculature. Direct
evidence of the role of the cranial muscles in de-
termining skull form in mammals is limited to the
effects of unilateral paralysis or removal of mus-
cles in young rats, rabbits, guinea pigs, and dogs.
Unilateral paralysis of the facial muscles (Wash-
burn, 1946a), removal of one masseter (Horowitz
and Shapiro, 1955, and earlier workers), of one
temporal (Washburn, 1947, and earlier workers),
or of neck muscles (Neubauer, 1925), all resulted
in asymmetrical development of the skull, with
failure of associated bony crests and ridges to form.
Removal of the temporal was followed by resorp-
tion of the coronoid process but did not alter the
internal form of the braincase. No one has re-
moved simultaneously the temporal, zygomatico-
mandibularis, and masseter from one side to deter-
mine the part played by these major muscles in
determining the form of the zygomatic arch; it is
very probable that bizygomatic breadth is inti-
mately related to these muscles.
These experiments were performed far too late
in ontogeny to provide the intimate knowledge of
the factors of embryogenesis we have for the limb
bones of the chick (Murray, 1936). So far as they
go, the experiments strongly reinforce the observa-
tional data of comparative anatomy. Practically
nothing is known of the development of the form
of the skull, but from what is known of develop-
ing limb bones in vertebrates (Murray, 1936; La-
croix, 1951) the primary form of both dermal and
cartilage bones of the skull is probably determined
by intrinsic growth patterns, whereas modeling is
determined by pressures and tensions extrinsic to
the bones, created by musculature, brain, sense
organs, vessels and nerves, and mechanical inter-
action between the developing bones themselves.
We may assume that, except for differences result-
ing from increase in volume of bone tissue, the
considerable differences in form between the skull
of the panda and that of the bears are largely,
perhaps almost entirely, dependent on such ex-
trinsic factors that of the cranium on the muscu-
lature, and that of the face on the dentition.
The only features for which intrinsic factors
must be postulated appear to be the tremendous
increase in the bone substance making up the skull
(by proliferation of connective tissue) and the ele-
vation of the mandibular articulation (by prolifer-
ation of cartilage). Elevation of the articulation
enhances horizontal movements of the mandible.
It occurs in some degree in all herbivorous mam-
mals and surely is a direct result of natural selec-
tion operating on the skull. The morphogenetic
mechanism whereby it is achieved is unknown,
but the fundamental similarity to the acromegalic
mandible suggests that it is simple.
We may conclude that no more than four, and
perhaps only three, factors were involved in the
transformation of the ursid type of skull into that
of Ailuropoda. Two of these hypertrophy of jaw
musculature and dentition are extrinsic to the
skull and therefore involve only the ability of
the bone to respond to mechanical stress. Two
general hypertrophy of bone substance and ele-
vation of the mandibular articulation are intrin-
sic to the skeleton but involve different growth
74
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
mechanisms. Thus only two factors acting di-
rectly on the skull itself may distinguish the skull
of Ailuropoda from that of other ursids. Natural
selection has no doubt had additional minor polish-
ing effects, although the whole morphology of the
giant panda indicates that the morphological in-
tegration produced by such refined selection is at
a relatively low level.
E. Summary of Skull
1. The skull of Ailuropoda is basically similar
to that of Ursus. Agreement is particularly close
in structures relatively unaffected by masticatory
requirements: the turbinates, the paranasal sinuses,
the middle ear, and the inner lamina of the cranial
cavity.
2. The outer lamina of the cranium and the
mandible are remarkable for the thickness and
density of the bone. This greatly exceeds mechan-
ical requirements, and therefore is not directly
adaptive.
3. All parts of the skull associated with the
masticatory apparatus are greatly expanded. The
volume of the temporal fossa in particular, espe-
cially its anterior third, has been increased at the
expense of surrounding structures. Similar adap-
tive changes appear convergently in Ailurus and,
in slightly altered form, in hyenas.
4. From the genetic standpoint these adaptive
changes are probably extrinsic to the bone itself,
involving only the ability of the bone to respond
to mechanical forces during ontogeny.
5. The only obvious intrinsic factors are the
great increase in bone tissue in the cranium and
mandible, and the elevation of the mandibular
articulation above the occlusal plane.
6. Thus only two major factors acting directly
on the skull itself may distinguish the skull of
Ailuropoda from that of Ursus.
7. Certain features usually regarded as diag-
nostic of the Ursidae (e.g., by Flower, 1869) have
been obliterated in Ailuropoda by the expansion
of the masticatory apparatus. Among these are
postorbital processes on frontal bones, presence of
alisphenoid canal, non-confluence of foramen ro-
tundum and orbital fissure, and presence of fora-
men lacerum medium. Such secondary differences
cannot be used as evidence of non-relationship be-
tween the panda and the bears.
IL THE VERTEBRAL COLUMN
A. The Vertebral Column as a Whole
The vertebral column of the giant panda is in
many respects the most remarkable among living
carnivores. Slijper (1946) showed that the archi-
tecture of the developing column is responsive to
the mechanical demands of posture and locomo-
tion. Morphogenetically the mammalian column
behaves like other homiotic structures (Kiihne,
1936; Sawin, 1945, 1946). Therefore it is prefer-
able to consider the column as a whole, rather than
as a chain of independent units. The analytical
study of the vertebrae of the Carnivora made by
Stromer von Reichenbach (1902) showed that the
morphological details of individual vertebae ex-
hibit no important features consistently correlated
with the major categories, and are therefore of
little systematic importance. For this reason no
detailed description and comparison of individual
vertebrae of Ailuropoda is presented here.
The number of presacral vertebrae is extremely
constant in carnivores. The normal number of
thoraco-lumbars in all living Carnivora is twenty,
and individual variations rarely exceed one above
or below this figure. The giant panda is conse-
quently remarkable in having only eighteen trunk
vertebrae; in one of nine skeletons this number
was further reduced to seventeen, and in one there
were nineteen (Table 9).
The number of lumbar vertebrae in Ailuropoda
is five in 50 per cent of the cases, and four in the
remaining 50 per cent; in Ursus it is six in 79 per
cent, and five in the remaining 21 per cent. (Other
genera of the Ursidae appear to differ from Ursus,
but the samples are too small to permit conclu-
sions.) The modal number of lumbars is either
four or five in Ailuropoda, and six in Ursus; the
mean is 4.5 and 5.8, respectively, indicating that
the lumbar region has been reduced by more than
one vertebra in Ailuropoda. The thoracics show
a similar but somewhat more limited tendency
toward reduction: the mean is 13.5 in Ailuropoda,
14.2 in Ursus. There was evidence of disturbance
at the cervico-thoracic boundary in one individual
(p. 85). Thus in the column as a whole there is
an anterior displacement of the boundaries of the
several regions in Ailuropoda, and this displace-
ment shows a gradient decreasing in intensity from
the sacrum toward the head.
A remarkable feature of the column in Ailuro-
poda is its variability. Of nine skeletons examined,
the thoraco-lumbar juncture was asymmetrical on
the two sides of the body in three, and four differ-
ent vertebral formulae are represented among the
remaining six individuals (Table 9). This varia-
bility is greater than was found in any of the nu-
merous arctoid and ailuroid carnivores examined.
The proportions of the three main divisions of
the column in Ailuropoda differ from those in other
carnivores, as shown below. These proportions
also show a far greater range of variation than in
DAVIS: THE GIANT PANDA
75
Table 9. VERTEBRAL COUNTS IN CARNIVORES
Number
of indi-
viduals
Cants latrans 15
Canis lupus / 9
Vulpes fulva / 9
Uroeyon cinereoargenteus I ,
Bassariscus astutus J j
1
Nasua narica 1
Nasua nasua 5
fll
Procyon lotor J 2
I 1
f ^
Bassaricyon alleni J 1
I i
Ailurus fulgens^ 5
Ursus (various species)^ 7
Ursus^ 2
C7rsus' 1
(2
Ailuropoda melanoleuca . 1 3
?
' One record from Flower (1885).
' Three records from Flower (1885).
any other carnivore examined. The cervical re-
gion is shorter in Ailuropoda than in Ursus but is
only slightly shorter than in Ailurus and Nasua
and no shorter than in Procyon. The thoracic re-
gion is relatively longer than in any other arctoid
carnivore, resembling that of burrowing mustelids.
The lumbar region is short in both Ailuropoda and
Ursus. The proportions of the vertebral colurnn
Thoracics
Thor-
+ lum-
acics
Lumbars
bars
13
7
20
13
7
20
14
7
21
13
7
20
13/14
7/6
20
13
7
20
13
6
19
13
7
20
13
6
19
13
5
18
15
5
20
15
5
20
14
6
20
15
20
14
19
13
6
19
13
7
20
14
7
21
14
6
20
14/13
6/7
20
14
6
20
14
6
20
15
5
20
14/15
6/5
20
14
5
19
14
4
18
14/13
4/5
18
13
5
18
13
4
17
of the giant panda are similar to those of the an-
thropoid apes and man, and to those of such bur-
rowing carnivores as Taxidea, Meles, and Mellivora
columns designed to withstand anteroposterior
thrust.
The vertebrae of Ailuropoda are heavier than in
Ursus; the weight of thoraco-lumbar vertebrae is
about 16 per cent greater in a specimen of the
panda than in a black bear of comparable size.
The Mechanics of the Vertebral Column
The vertebral column of mammals, with its as-
sociated muscles and ligaments, is an extremely
complex mechanism that has never been satisfac-
torily analyzed. Yet it is only on the basis of its
functioning that the differences, often extremely
subtle, exhibited in this region from animal to ani-
mal can be intelligently considered. Slijper (1946)
made a painstaking comparative study of the col-
umn in mammals in an effort to correlate mor-
phology and function. Many of his findings are
relevant in the present connection.
Slijper rejects former comparisons of the verte-
bral column with an arched roof, a bridge with
parallel girders, or a cantilever bridge, and com-
pares it with a bow flexed by a bow-string (the
sternum, abdominal muscles, and linea alba).
Vertebral Bodies. Slijper points out that the
principal static function of the column is to resist
bending, chiefly in the sagittal plane, and that
differences in the size and shape of the vertebral
bodies reflect the forces acting on them. He used
as a criterion of the stress to which any part of
the column is subjected the moment of resistance
to bending, which he computed for each vertebral
body by using the formula: breadth of articular
face of body X square of height of body (bh-).
Plotting these data for the entire column in a series
of mammals yields characteristic curves of the
moments of resistance at successive points along
Table 10. RELATIVE PROPORTIONS OF DIVISIONS OF THE VERTEBRAL COLUMN IN CARNIVORES'
N Cervical (%) Thoracic (%) Lumbar (%)
Canis 2 30 39.5(39-40) 30.5(30-31)
Vulpes 2 28.8 (28-29.5) 39.8 (39.5-40) 31.5
Bassariscus 1 24 42 34
Nasua 1 22 45 33
Procyon 4 21.4 (21-22) 47.7 (47-48) 30.9 (30-31.5)
Ailurus 3 22 (21.3-22) 47 (47-47.5) 31 (31.0-31.2)
Ursus 3 26.2 (25.5-27.4) 45.9 (45.6-46.3) 27.9 (26.3-28.9)
Ailuropoda 6 22 (21-23.2) 55 (51.7-59) 23 (20-26)
Taxidea 2 23 50.5 (50-51) 26.5 (26-27)
Meles 1 25 53 22
Mellivora 1 25 56 19
' Ursus and Ailuropoda determined on disarticulated skeletons.
76
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
ITh
r-
IL
B
ITh
1^
IL
Fig. 33. Diagrams of moments of resistance in the vertebral columns of various mammals:
A. Moments of resistance in a beam supported at one end.
B. Slijper's Type 16 curve of moments of resistance in the vertebral column of mammals with an erect or semi-erect
posture (compare with A and fig. 34).
C. Theoretical moments of resistance in quadrupedal mammals, in which the vertebral column is compared to a bow,
with a beam supported at one end attached to the cranial (left) end of the bow.
D. Slijper's Type II curve of moments of resistance in the vertebral column, characteristic of carnivores other than bears
and Ailuropoda (compare with C).
the column. Slijper divides these curves into three
major types, each with several subtypes.
Of the few carnivores examined by Slijper (Ca-
ms, Vulpes, Ursus, Felis, Panther a), all except
Ursus yielded curves of Type II, characterized by
a hump in the posterior cervical region, and a flat
anterior thoracic region, followed by a rise in the
posterior thoracic and lumbar regions (fig. 33, D).'
For Ursus the curve slopes upward gradually from
the anterior cervical region to about the tenth
thoracic, then abruptly breaks more steeply up-
ward, sloping downward again in the posterior
lumbar region. This is Slijper's Type lb curve,
characteristic of bipedal animals, including man
(fig. 33, B). The curve for Slijper's bipedal goat
was also modified in this direction. This type of
curve agrees closely with the diagram of the theo-
retical moments of resistance if the column is re-
garded as an erect or semi-erect beam supported
at one end (fig. 33, A).
The curve of the moments of resistance for Ai-
luropoda was plotted for two individuals, which
showed only minor differences (fig. 34) . This curve
is very similar to that for Ursus, differing chiefly
' Slijper lists the domestic cat (along with the bear and
the anthropoid apes and man) as having a Type lb curve.
This is obviously a mistake. I have measured and plotted
a disarticulated cat column, and find that it has a typical
Type II curve.
in its more even slope without the sharp upward
break at the level of the diaphragmatic vertebra
(eleventh thoracic in Ursus, eleventh or twelfth in
Ailuropoda). In this respect Ailuropoda resem-
bles the anthropoid apes and man more closely
than Ursus does.
It is evident that the vertebral axis in the bears,
and especially in the giant panda, is constructed
to withstand anteroposterior thrust.
Neural Spines. The length and angle of in-
clination of the neural spines do not depend upon
the static demands made upon the column, but
upon the structure and development of the epaxial
muscles that attach to them (Slijper). Thus the
structure of the spines is ultimately determined by
posture and locomotion, plus such secondary fac-
tors as absolute body size, length of neck, and
weight of head. Both length and inclination of a
spine are resultants of the several forces exerted
by the muscles attaching to it, the spine acting as
a lever transmitting the muscle force to the ver-
tebral body.
Plotting the lengths of neural spines as percent-
ages of trunk length permits comparison of the
resulting curves for various animals. These curves
apparently follow a common pattern in all mam-
mals, although the relative lengths of the spines
DAVIS: THE GIANT PANDA
77
SOr
40
30
SO
bh
n4IO*
36759 Ailuropoda melanoleuca
3I0<
2I0*
C'3
Th-l
10
L-l
Fig. 34. Curve showing height (h), breadth (6), and moments of resistance (b/i') in the vertebral column of Ailuropoda.
D = diaphragmatic vertebra.
vary greatly from species to species. The spines
are longest on the anterior thoracic vertebrae (at-
tachment of cervical muscles and ligaments), de-
crease in length back to the anticlinal or diaphrag-
matic vertebra, and are slightly longer again on
the posterior thoracic and lumbar vertebrae (at-
tachment of longissimus and spinalis muscles).
Both Ursus and Ailuropoda exhibit this type of
curve, although in both forms the spines are rela-
tively short along the whole length of the column
(fig. 35).
The inclination of the spines conforms less closely
to a common pattern than does the height. Ac-
cording to Slijper the direction of a given spine
tends, for mechanical reasons, to be perpendicular
to the most important muscle inserting into it.
The spines of the pre-anticlinal (or pre-diaphrag-
matic) vertebrae are inclined posteriorly in all car-
nivores, as they are in all mammals. Among the
arctoid Carnivora the post-diaphragmatic spines
are inclined anteriorly in the Canidae and Procy-
onidae, are variable among the Mustelidae (from
an anterior inclination of 45 in the martens to a
slight posterior inclination in the skunks and
badgers), and are posteriorly inclined or at most
vertical in the Ursidae. In Ailuropoda all the
post-diaphragmatic vertebrae are posteriorly in-
clined, the minimum inclination in two skeletons
being 20 (fig. 36). According to Slijper the direc-
tion of the post-diaphragmatic spines in Carnivora
and Primates is determined chiefly by the length
of the vertebral bodies, because the angle of at-
tachment of the multifidus muscle depends upon
this length. The bodies of the lumbar vertebrae
are short in both giant panda and bears, but they
are not notably shorter in Ailuropoda than in Ur-
sus, although the posterior inclination of the spines
is much greater. Thus, other factors must be in-
volved in Ailuropoda. It is at least suggestive that
among the primates and burrowing mustelids a pos-
terior inclination of the post-diaphragmatic spines
is associated with anteroposterior thrust along the
column.
78
FIELDIAXA: ZOOLOGY MEMOIRS, VOLUME 3
% of length of trunk
13
LENGTH OF NEURAL SPINES
\Canis
(from Slijper)
"Ailuropoda
2 3
Vertebrae
K) n
12 13
Fig. 33. Curves showing lengths of neural spines in AUnropoda, Ursus arHof, and Canig familiaris.
B. DE:scRipnoNS of Vertebrae
1. Cervical Vertebrae
The cervical vertebrae in Ailuropoda are remark-
able for their breadth, which gives the cervical
region a compressed appearance, especially when
viewed from below. Transverse broadening is evi-
dent on all vertebrae including the atlas and epi-
stropheus, and greatly exceeds that in any other
land carnivore. The vertebrae are shorter antero-
posteriorly than in the long-necked Ursus, but are
no shorter than in Proeyon and Ailurus. There
are seven cervicals in each of the eight skeletons
examined.
Except for the distortion resulting from broad-
ening, the cervicals differ little from those of other
carnivores. The atlas is similar to that of Ursus
in the arrangement of foramina; in both there is
an alar foramen < vertebral artery and vein>, in-
stead of a mere notch as in other arctoids, into
which open the atlantal foramen dntervertebral
of authors; transmits first spinal nerve and verte-
DAVIS: THE GIANT PANDA
79
Degrees
30
INCLINATION OF NEURAL SPINES
Ailuropoda
I 2 3 4 5 6 7
Thoraco Lumbar Vertebrae
20 21
Fig. 36. Curves showing inclination of neural spines in Ailuropoda, Ursus arctos, and Canis familiaris.
bral artery) and transverse foramen (vertebral ar-
tery and vein). The foramina on the atlas are
crowded together as compared with Ursus (fig. 37).
The transverse diameter across the wings is greater
than in Ursus, but the wings are narrower antero-
posteriorly.
The third to sixth cervicals are notable chiefly
for the conspicuous, backwardly directed hypera-
pophysis (Mivart) atop each postzygopophysis;
these are barely indicated in Ursus, and are want-
ing in other arctoids. The spines are nearly obso-
lete on the third, fourth, and fifth cervicals, but
are of normal length on the sixth and seventh.
2. Thoracic Vertebrae
The thoracic region in Ailuropoda is notable for
its length. Since the number of thoracic verte-
brae averages about one less than in Ursus, the
gi-oater thoracic' length must be attributed to
longer centra on individual vertebrae, but I have
been unable to demonstrate this satisfactorily.
There is, of course, no anticlinal vertebra in
Ailuropoda, since the neural spines all slope in the
same direction. A true anticlinal is also wanting
in Urstis for the same reason. The diaphragmatic
vertebra is that transitional vertebra on which the
prezygapophyseal facets look upward (horizontal),
while the postzygapophyseal facets look outward
(vertical or oblique) . The diaphragmatic vertebra
is the eleventh thoracic in one specimen of Ailu-
' This length of thorax is approached or even exceeded in
some burrowing mustelids, e.g., Taxidea, Mephitis, Melli-
vora. In these forms, however, the thoracic region has taken
over the anterior lumbars, and the thoracic count is 1 6 or 1 7.
For. atlantis
For. alare
Ala atlantis
For. Iransversarium
B
For. transversarium'
Corpus epistropheus
Ailuropoda
Ursus americanus
Fig. 37. Cervical vertebrae of Ailuropoda and Ursus. A, atlas from below; B, epistropheus and third cervical from left side.
anterior
lateral
Fig. 38. Fifth thoracic vertebra of Ailuropoda.
posterior
80
DAVIS: THE GIANT PANDA
81
ropoda, the twelfth in another. It is the eleventh
in Ursus. It is uniformly Th. 10 in the Canidae.
The Procyonidae vary: Bassariscus, Th. 10; Bas-
saricyon, Th. 10; Ailurus, Th. 11; Procyon and
Nasua, Th. 12.
There are fewer lumbar vertebrae (an average
of 4.5 in the eight skeletons examined) than in any
other arctoid carnivore. ^ The lumbar spines all
slope posteriorly; this is not encountered in any
other arctoid, but is approached in Ursus.
Ailuropoda
UrsKs americanus
Fig. 39. Third lumbar vertebra of Ailuropoda and fourth lumbar of Ursus, seen from the left.
There are few significant differences in morpho-
logical details. The intervertebral foramina (spi-
nal nerves and vessels) are conspicuously larger
than in Ursus, owing chiefly to the larger size of
the posterior vertebral notch. The width across
prezygapophyses and postzygapophyses is much
greater in Ailuropoda than in Ursus and other
arctoids, which should contribute to the stability
of this region. The spines are capitate, especially
on the anterior vertebrae. Their posterior bor-
ders are less produced than in Ursus, and their
lateral surfaces present prominent muscle rugo-
sities that are lacking in other arctoids.
3. Lumbar Vertebrae
The lumbar region is shorter than in any other
arctoid carnivore examined. It is short in burrow-
ing mustelids (Meles 22 per cent, Mellivora 19 per
cent, but Taxidea 26-27 per cent) and hyenas (18-
20 per cent). The length relative to the total col-
umn is not much greater in Ursus than in Ailuro-
poda (see Table 10) , but because of the long neck in
bears this does not properly reflect the true short-
ness of the lumbar region in Ailuropoda. The
absolute length of the lumbar region in Ailuropoda
is only 165-180 mm. (32-33 per cent of thoraco-
lumbar length), while in a bear of comparable size
(Ursus americanus) it measures 233 mm. (38 per
cent of thoraco-lumbar length).
The form of the vertebrae is similar to that in
Ursus. The centra are very short in both. As
with the thoracics, the intervertebral foramina are
larger, and the pre- and postzygapophyses are wider
than in Ursus.
The lumbar spines in both the giant panda and
the bears are short and stumpy, and are either ver-
tical (Ursus) or posteriorly inclined (Ailuropoda).
Slijper believes that the vertical position of the
spines in Ursus is correlated with the shortness of
the lumbar centra, which results in greater me-
chanical efficiency in the longissimus and multifi-
dus muscles attaching to them.
The transverse proces.ses are not well developed
in either Ailuropoda or Ursus. In both they are
relatively short, and directed transversely instead
of anteriorly as in other arctoids. These processes
provide attachment for the ilio-costal and quad-
ratus lumborum muscles, which function in exten-
sion and flexion of the column and hence are
important in movements of the back during run-
ning.
Anapophyses (accessory process of Reighard and
Jennings and Baum and Zietzschmann) are pres-
' In some of the burrowing mustelids (Arctonyr, Cone-
paius, Mellivora) four is apparently the normal number of
lumbars. In these, however, the number of thoracics is cor-
respondingly increased, and the thoraco-lumbar count is 20
or 21, the typical carnivore formula. The curve of the
moments of resistance is also altogether different.
82
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
ent on the first two lumbars, are barely indicated
on the third, and are obsolete on succeeding verte-
brae. Ursus is practically identical. These proc-
esses are present on all lumbars except the last in
Procyon and Nasua, and on all but the last two in
Four pelves of Ailuropoda were available for de-
tailed examination. Three full vertebrae are in-
volved in the sacro-iliac joint in two, and two and
a part of the third are involved in two individuals.
In one sacrum articulating by three full vertebrae.
Proc. spinosus
Praezygapophysis
MC Postzygapophysis
Anapophysis
Proc. tramrersus
Ailuropoda
Ursus
Fig. 40. Second lumbar vertebra of Ailuropoda and Ursus americanus, seen from the rear.
other procyonids and Canis. They provide inser-
tion for the tendons of the longissimus muscle,
which functions in extension and flexion move-
ments of the vertebral column.
4. Sacral Vertebrae
The sacrum is composed of five fused vertebrae
in all eight skeletons of Ailuropoda examined. As
will be seen from the accompanying table, Ursus
is remarkably varied in this respect, although the
most frequent number is likewise five. In all other
arctoid carnivores the normal number of sacrals is
three. (Sacrals are reckoned, according to the
definition of Schultz and Straus, as "the vertebrae
composing the sacrum and possessing interverte-
bral and sacral foramina ringed completely by
bone in the adult.")
Number of Sacral Vertebrae
Canis latrans
Canis lupus
Vulpes fulva
Urocyon cinereoargentetis .
Bassariscus astutus
Nasua narica
Nasua nasua
Procyon lotor
Bassaricyon alleni
Ailurus fulgens*
Ursus sp.**
Ailuropoda melanoleuca. .
S
14
10
10
5
7
1
5
13
6
5
1
* One record from Flower. ** Six records from Flower.
the first sacral has the appearance of a transformed
lumbar well-formed pre- and postzygapophyses,
enormous sacral foramina, incomplete fusion of the
centra ventrally although on the basis of the total
column it is numerically equivalent to the first sa-
cral of the second individual. This is of interest in
connection with the reduced number of thoraco-
lumbars in Ailuropoda, and the extraordinary in-
stability of the thoraco-lumbar boundary. It is
further evidence of the genetic instability of the
posterior part of the vertebral column in this
species.
In the primary condition in arctoids, as seen in
Canis, Bassariscus, and Nasua, the sacro-iliac ar-
ticulation is restricted almost entirely to a single
vertebra, the first sacral. In Procyon and Urstts
the articulation is more extensive, including the
first two sacrals, while in Ailuropoda it reaches
its maximum among the arctoid carnivores with
the third vertebra participating more or less com-
pletely.
It is interesting and suggestive that the increase
in length of sacrum and extent of sacro-iliac artic-
ulation among the Carnivora is paralleled among
the Primates. The figures given by Schultz and
Straus (1945) show that the number of sacrals in-
creases abruptly in the anthropoid apes and man
over the number found in other Primates (except
the aberrant Lorisinae). Examination of a series
of primate skeletons shows that the extent of the
sacro-iliac articulation is likewise increased in the
bipedal apes and man.
DAVIS: THE GIANT PANDA
83
Praezygapophysis
Arnis rertebrae
Proc: transrersus
PostzygapophysU
lsl,2nd & 3rd Caudals
Isl.Znd & 3rd Caudals
lst,gnd & Srd Caudals
6th Caudal
6th Caudal
6th Caudal
1st Caudal (anterior)
Ailuropoda
1st Caudal (anterior)
Ursns
1st Caudal (anterior)
Procyon
Fig. 41. Caudal vertebrae of Ailuropoda, Ursus americanus, and Procyon lotor. First three caudals, dorsal view; sixth
caudal, dorsal view.
The morphology of the sacrum in Ailuropoda is
similar to that of Ursus but differs in a number of
respects. The long axis of the bone is nearly
straight in the panda, while in the bears it is
slightly curved ventrad. In the panda the sacrum,
like the remainder of the vertebral column, ap-
pears to be expanded laterally and depressed dorso-
ventrally. The spines are fused to form a contin-
uous median sacral crest, which forms a peak on
the first sacral and becomes nearly or quite obso-
lete on the fifth. The intervertebral foramina are
minute, irregular, and nearly obliterated. There
are four pairs of dorsal sacral foramina (dorsal
divisions of sacral nerves, branches of lateral sa-
cral arteries). The first two pairs are irregular,
often small and almost obliterated as a result of
bone growth in connection with the sacro-iliac an-
kylosis. The last two pairs are larger and more
regular. The four pairs of ventral sacral foramina
(ventral divisions of sacral nerves, branches of
lateral sacral arteries) are much larger and more
regular than the dorsal foramina.
5. Caudal Vertebrae
The tail is short and almost vestigial, but neither
as short nor as degenerate as in the bears.
Nowhere is the shortening and dorso-ventral
flattening of all the vertebrae of Ailuropoda more
apparent than in the tail. All the caudals are
heavy and stocky; even those toward the tip of
the tail lack the slender rod-like form characteris-
tic of other carnivores. This is undoubtedly to be
interpreted as a gratuitous extension of the factors
influencing the remainder of the column, since in
Ailuropoda, as in the bears, the tail is functionless.
The tail is composed of eleven vertebrae in the
one specimen in which it is complete. This is
within the range of variation of Ursus, in which
there are eight to eleven or more vertebrae. Other
arctoids have much longer tails, with from eighteen
to twenty or more vertebrae, each of which is rela-
tively much longer than in Ailuropoda or Ursus.
The first two caudals are well formed in Ailur-
opoda, with complete neural arch but no neural
spine, wide transverse processes, and prezyga-
pophyses; postzygapophyses, which are present
in other arctoids except Ursus, are wanting. On
the first vertebra the transverse processes extend
the entire length of the centrum, and even ante-
riorly beyond the centrum onto the prezygapophy-
sis. There are no chevron bones. In Ursus, in
84
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
contrast, the neural arches are wanting on all
caudals (U. americanus) or are present on only
the first vertebra, and the transverse processes are
almost completely obsolete even on the first cau-
dal. Chevron bones are wanting in the bears.
Viewed from the front, the first caudal exhibits
to a striking degree the dorso-ventral flattening
of the vertebrae (fig. 41).
The remaining caudals are short and stocky, ex-
hibiting less of the typical rod-like form than is
seen even in Ursus. The broadening effect is evi-
dent at least back to the seventh vertebra, the
transverse processes becoming entirely obsolete on
the eighth.
C. Review of the Vertebral Column
The contrast between Gadow's explanation of
the evolution of the vertebral column (1933) and
that of Slijper (1946) is a measure of the altered
point of view with respect to this complex struc-
ture. To Gadow the column is a series of discrete
entities, each with its own almost independent
phylogenetic history. A lumbar vertebra is fun-
damentally a lumbar, regardless of whether it has
been "transformed" into a thoracic in one instance
or a sacral in another. The functioning of the
column, as well as mechanisms by which observed
differences could have been achieved, are ignored.
The goal is to discover the "true homologies" of
elements a goal that, with respect to the verte-
brae, we now know is largely a will-o'-the-wisp.
This is the classical outlook of many of the older
comparative anatomists.
Slijper, on the other hand, has regarded the col-
umn, along with its muscles and ligaments, as an
architectural construction responsive to the me-
chanical demands of posture and locomotion. He
has tried to determine correlations between struc-
ture and function under varying conditions. Ho-
mologies are not considered. His work is essentially
an engineering study.
Neither Gadow nor Slijper considered the ques-
tion of how, from the standpoint of evolutionary
mechanisms, the differences they observed could
have been brought about. Studies by Kiihne
(1936) and others on the inheritance of variations
in the human vertebral column showed that dif-
ferentiation of the column, like that of other homi-
otic structures, is genetically controlled as a series
of fields or gradients of differentiation and growth.
These fields correspond to the thoracic, lumbar,
and sacral regions of the column. The anlage of
a vertebra is indifferent; its differentiated form
depends on its position in a particular field. There
is also a general cranio-caudal gradient of differen-
tiation; so increasing the tempo of development
would shift the boundaries of all regions cranially,
and vice versa. Kuhne emphasized that all dis-
placements were always in the same direction in a
given individual. Moreover, "besides the trunk
skeleton, the field of action embraces the periph-
eral nervous system (limb plexuses), musculature,
blood vessels, and a large part of the organs of the
thoracic and abdominal cavities" (Kiihne). Kiihne
concluded that all the variations he observed could
be explained by assuming a single pair of alleles,
"craniad" and "caudad." These deductions were
verified experimentally by Sawin (1945, 1946),
who concluded from breeding experiments on rab-
bits that displacements of the boundaries of verte-
bral regions are determined primarily by a single
pair of genes.
Among the arctoid carnivores the thoracolum-
bar boundary is shifted caudad in the Procyonidae
(except the primitive Bassariscus) and Ursidae.
The functional significance, if any, of this shift is
unknown. It did not affect the number of thoraco-
lumbar segments, which remain at the typical 20.
In Ailuropoda the thoracolumbar boundary is vari-
able, but obviously has been shifted cranially from
its position in the Ursidae. The lumbosacral
boundary has likewise been shifted cranially two
to three vertebrae from its typical position in arc-
toid carnivores. Thus in Ailuropoda, as in the
higher primates, there is a general cranial displace-
ment in the regional boundaries of the column.
In both the panda and the higher primates this
cranial shift is associated with intense differentia-
tion in the anteriormost part of the body axis
the head. In both cases this "cephalization" rep-
resents an increase in the tempo of differentiation
or growth, although very different tissues are in-
volved. Because of the axial gradient, the cepha-
lization is accompanied by a cranial shift in the
boundaries of the regions of the column. Conse-
quently, shortening of the column and displace-
ment of its regional boundaries in Ailuropoda (and
probably also in the higher primates) are not
themselves adaptive, but are consequential results
of a process of cephalization. In bulldogs, which
are likewise characterized by cephalization, Klatt
and Oboussier (1951) reported malformations of
the vertebral column (but no reduction in num-
ber of vertebrae) in about 80 per cent of their
specimens.
The vertebrae are also broadened and depressed
in Ailuropoda in comparison with Ursus and other
carnivores. There is no way of determining how
much this is due to secondary postnatal factors
extrinsic to the bone itself, although there is no
evidence that the condition is adaptive. The facts
DAVIS: THE GIANT PANDA
85
that it is markedly evident in the tail, where the
static influences of posture and locomotion do not
exist, and that the same effect is evident on the
proximal ends of the ribs, strongly suggest that
this is a part of the field effect involving the entire
axial region of the body.
Homiotic variability in the column of Ailuro-
poda is greater than in any other carnivore exam-
ined. This indicates that the mechanism regulating
differentiation of the column is not yet stabilized
around a new norm, which in turn suggests an
absence of strong selection pressure on this region.
Thus the vertebral column of Ailuropoda differs
from that of Ursus in several respects. The dif-
ferences are not random, but rather form some
kind of pattern. We must assume as a working
hypothesis that the differences are adaptive that
they are a product of natural selection. We then
seek answers to two questions: (1) what is their
functional significance, and (2) what morphoge-
netic mechanism, intrinsic to the bone tissue, lies
behind them?
It has been noted repeatedly throughout the
description that the column of Ailuropoda resem-
bles columns designed to withstand strong thrust
forces acting anteroposteriorly in the direction of
the sacrum. Among terrestrial mammals such
forces, and correlated modifications of the column,
occur only in fossorial and bipedal forms. The
work of Slijper shows that the mammalian column
responds adaptively to such forces, even non-
genetically. Ailuropoda is, of course, in no way
fossorial; and it is no more bipedal than the bears,
in which the column shows slight almost trivial
compared with that in Ailuropoda convergence
toward the column of truly bipedal forms. The
column of Ailuropoda cannot be explained on the
basis of mechanical requirements, and therefore
the differences from Ursus cannot be attributed to
natural selection acting on the column. The seem-
ingly adaptive modifications must be "pseudo-
adaptations."
The data of Sawin and Hull suggest an alterna-
tive explanation. All those areas of a tissue that
are in a state of competence at a given moment
during ontogeny are known to be affected by a
genetic factor operating at that moment. Thus
the lumbosacral peculiarities of Ailuropoda may
reflect an accident of ontogenetic timing rather
than the action of selection on the lumbar region.
If the differentiating lumbar region were compe-
tent at the same moment as some other region on
which selection was acting strongly (e.g., the skull),
then in the absence of strong selection against the
induced lumbar modifications, such modifications
would be carried as a pleiotropic effect. If they
were strongly selected against they would presum-
ably be buffered out. The extraordinary homiotic
variability of the lumbosacral region in Ailuropoda
supports this interpretation, as does the otherwise
unintelligible modification of the pelvis (p. 113).
On the basis of the available evidence it must
be concluded that primary differences between the
column of Ailuropoda and that of Ursus are not
adaptive, but represent a pleiotropic effect result-
ing from an accident of ontogenetic timing. The
genetic basis for such an effect is probably very
simple.
D. Conclusions
1. The vertebral column of Ailuropoda differs
from that of Ursus (and other arctoid carnivores)
in several important respects.
(a) The regional boundaries are shifted crani-
ally in a gradient that decreases in intensity
from the lumbosacral boundary (greatest)
to the thoracocervical (least).
(b) All vertebrae are broadened and depressed.
(c) Homiotic variability exceeds that known
in any other carnivore.
2. The differences are not adaptive.
3. The differences are associated with intensi-
fied growth at the anterior end of the body axis
the head. Similar correlations are evident in pri-
mates and in bulldogs.
4. The characteristic basic features of the ver-
tebral column in Ailuropoda are a pleiotropic effect
resulting from an accident of ontogenetic timing.
V. THE THORAX
The thoracic region, as pointed out above, is
relatively longer in Ailuropoda than in any other
arctoid carnivore. This is true when the extent
of the thorax is measured dorsally, along the ver-
tebral column. On the other hand the ventral
length of the thorax, measured along the sternum,
is notably less than in any other arctoid carnivore.
A. Ribs
The number of ribs varies between 13 and 14
pairs in the eight skeletons examined, with a high
proportion of asymmetries on the two sides of the
same animal (see Table 9, p. 75). On the basis of
the available material it is impossible to determine
which is the typical number.
In one skeleton (31128), which shows other gross
abnormalities, the first rib on the left side is short,
not reaching the manubrium, and the tubercular
head is pathological. The second rib resembles the
first of the opposite side, but its sternal end is
86
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
bifurcate and attaches to the manubrium by a
wide bifurcate costal cartilage.
of the sternum in this animal. In Su Lin two pairs
of the false ribs are floating.
Ailurvpoda ^"*
Fig. 42. Tenth rib, lateral view. Above, posterior views of heads of same ribs.
In two skeletons there are nine pairs of true ribs,
which is the normal number for arctoid carnivores.
The eighth and ninth pairs are not attached to
sternebrae in Ailuropoda, however; instead, the
ends of the sternal cartilages of each pair meet at
the ventral midline, ventral of the xiphoid carti-
lage. This is obviously a result of the shortening
The first costal cartilage is about 20 mm. long,
the ninth about 230 mm., in Su Lin. In an adult
the costal cartilages are very heavily calcified, with
coarse granular deposits appearing on the surface.
The ribs are very similar in length and curvature
to those of bears of comparable size ( Ursus ameri-
canus). All the ribs are remarkable, however, for
DAVIS: THE GIANT PANDA
87
a
f
\ I ff /
Fig. 43. Approximate area of maximal increase in thickness of cortical bone in Ailuropoda.
the immense bulk of their vertebral ends (fig. 42).
The transverse diameter of the neck of a given rib
in Ailuropoda is at least twice the diameter in
Ursus americanus. The disparity becomes in-
creasingly less toward the sternal end of the rib,
until the sternal third is no larger in the panda
than in the bear. It is at least suggestive that the
maximum broadening is in that part of the rib
closest to the vertebra, where, as we have seen, a
pronounced broadening effect is apparent, and
that the width gradually decreases to normal as
we move along the rib away from the vertebra.
B. Sternum
The sternum is composed of a short body and
an extremely long xiphoid cartilage. The body is
about 55 per cent of the length of the thorax in
88
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Ailuropoda, while in other arctoids it is from 75
to 100 per cent.
There are six sternebrae (including the manu-
brium) in each of three skeletons of Ailuropoda
examined. In other arctoids there are nine, ex-
cept in the Canidae, which usually have only eight.
All the sternebrae are short.
The manubrium is short, compared with that
of Ursus and other arctoids, and is relatively wider
transversely. In other arctoids this bone is pro-
duced anteriorly into a point, so that the outline
is similar to a spear head. This point is much less
evident in Ailuropoda, and in one of three speci-
mens is totally lacking so that the anterior border
of the manubrium is truncated. A single pair of
costal cartilages articulates with the manubrium.
The remaining sternebrae, five in number, are
short and spool-shaped, rectangular in cross sec-
tion. The first four measure about 25 mm. in
length, the fifth about 20 mm.
The xiphisternum is a remarkably long (120
mm.) cartilaginous rod, tapering gradually to a
point. It provides attachment for the sternal part
of the diaphragm and the posterior elements of the
transverse thoracic muscle. Elongation of the
xiphisternum appears to be a compensation for
the shortness of the bod^'^ of the sternum, since the
origin of the sternal part of the diaphragm is thus
brought into line with the origin of the costal part
of this muscle.
In the Canidae and Procyonidae the xiphister-
num is composed of an ossified rod ending in an
expanded flattened cartilage. In the Ui*sidae it is
a cartilaginous rod, with an ossicle of variable size
embedded in the anterior end.
In the Procyonidae the last stemebra is only
about half the thickness of those preceding it, pro-
ducing a "step" in the sternum. The last costal
cartilages meet their fellows beneath this bone, in-
stead of inserting into its lateral edges as they
normally do. A similar condition is often seen in
bears, in which this stemebra may be entirelj* un-
ossified. The posterior end of the sternum seems
to be undergoing regression in this group.
C. Review of the Thorax
Two points are of interest in the bones of the
thorax: the extraordinary expansion of the prox-
imal ends of the ribs, and the shortening of the
sternum.
No mechanical advantage can be assigned to
the rib condition. It is most easily explained as
an extension of the morphogenetic field effect that
is oi>erating on the adjoining vertebrae, and hence
without functional significance as far as the ribs
are concerned. Thus a region of increased bone
deposition extends the entire length of the head
and body and extends laterally over the proximal
two-thirds of the rib cage (fig. 43). Since the cor-
tex of the long bones is also thickened, the effect
is general over the entire skeleton though reduced
peripherally. An astonishingly similar condition
is seen in the ribs of the Triassic marine nothosaur
Pachypleurosaurus (1931, Peyer, Abh. Schweiz.
Paleont. Ges., 51, pi. 25; 1935, Zangerl, op. cit.,
56, fig. 23). In the reptile, enlargement of the
proximal ends of the ribs is associated with pachy-
ostosis; there is no evidence of this in Ailuropoda.
The extreme shortening of the sternum seen in
Ailuropoda is foreshadowed in the related procyo-
nids and bears, in which a tendency toward re-
duction from the rear forward is evident. There
is no obvious mechanical advantage to this shift,
which is inversely correlated with elongation of
the thorax in these animals. The sternum has
been shortened repeatedly in various mammalian
lines, but to my knowledge this has never been
studied from the standpoint of animal mechanics.
We may conclude, provisionally, that (1) the
broadening of the vertebral column has extended mor-
phogenetically to the proximal ends of the ribs in
Ailuropoda, and (2) the shortening of the sternum is
the final expression of a trend, of unknown signifi-
cance, seen in related forms.
VI. THE FORE LEG
In the giant panda, the bears, and the procyo-
nids the fore legs are used for manipulating objects,
especially during feeding, to a far greater extent
than in other carnivores. This requires a wider
range of movement, particularly of abduction of
the humerus and rotation of the fore arm, than in
tj-pical carnivores. All these forms are also more
or less arboreal, and in the heavier forms at least
this has profoundly altered the architecture of the
shoulder and fore leg (Davis, 1949i. Such uses of
the fore limb are secondary ; in the primary carni-
vore condition the fore leg is modified for cursorial
locomotion, and the structure of the limb in all
carnivores has been conditioned by this fact.
A. Bones of the Fore Leg
The clavicle is vestigial or absent in all Car-
nivora, never reaching either the acromion or the
sternum when a clavicle is present. Among the Arc-
toidea it is normally absent in Canis, exceptionally
being represented by a small nodule of cartilage
or bone (Ellenbei-ger and Baum). It is present as
a small spicule of bone embedded in the cephalo-
humeral muscle in Bassariscus, Procyon, and Ailu-
rus. It is completely wanting in the Ursidae, and
M. rhomboideus
M. rhomboideus capitis
M. rhomboideus
M. infraspinatus
M. acromiotrap. +
M. spinotrap.
M. teres major
M. subscapularis minor
M. supraspin.
M. triceps longus
M. teres minor/
M. spinodeltoideus''
M. biceps
M. atlantoscapularis
M. acromiodelt.
Fig. 44. Right scapula of Ailuropoda, lateral view. A, right scapula of Ursus areios.
M. rhomboideus
M. subscapularis
M. coracobrachialis
M. levator scapulae +
M. serratus ventralis
M. teres major
M. triceps longm
Fig. 45. Right scapula of Ailuropoda, medial view.
89
90
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
there is no indication of a clavicle in Ailuropoda.
The clavicle is less degenerate in the Feloidea.
1. Scapula
It has been stated repeatedly that the scapula
is influenced by muscular action probably to a
greater degree than any other bone in the body.
Dependence of scapula shape on muscle function
has been demonstrated experimentally for rats
(Wolff son, 1950). The forces involved in molding
the scapula are extremely complex, no fewer than
17 muscles arising or inserting on the scapula in
carnivores, and interpretation of differences in
scapular form is difficult. No adequate study of
the I'elation between form and function of the
mammalian scapula exists, although such a study
was attempted by Reinhardt (1929).
The scapula of the giant panda appears at first
glance to be quite strikingly different from that of
any other arctoid. This is due to the unorthodox
outline of the bone (fig. 44). Actually, all the
features that distinguish the scapula of Ursus from
other arctoids are also present in Ailuropoda, al-
though the large postscapular fossa of the bears
is reduced in the panda. These ursid features
are: prominent postscapular fossa, large table-like
acromion with poorly differentiated metacromion,
breadth of neck exceeding long diameter of glenoid
fossa, well-defined spiral groove on axillary border,
and narrow glenoid cavity. There can be no doubt
that the scapula of the giant panda is basically a
bear scapula.
I have tried to show (Davis, 1949) that the
shoulder architecture of bears, and hence the form
of the scapula, is adapted to resist pulling forces
(the opposite of the thrust associated with normal
locomotion) developed in connection with climb-
ing, the morphological effects of which are exag-
gerated because of the size of the animal. The
tremendous postscapular fossa, from which the
subscapularis minor muscle arises, is the most con-
spicuous feature associated with this reversed force
direction; it is even larger in such powerful diggers
as the anteaters and armadillos, in which similar
pulling forces are involved.
The posterior angle (and thus the scapular in-
dex) is influenced chiefly by the posterior part of
the serratus ventralis muscle. This part of the
serratus is a posterior rotator of the scapula, and
is used in protraction of the arm (A. B. Howell,
1926). The posterior part of the serratus is well
developed in Ailuropoda, and this may account,
at least in part, for the pulling out of the poste-
rior angle.
Morphology. The scapula of Ailuropoda is
more fan-shaped than the almost rectangular scap-
ula of Ursus. Of the three borders, the coracoid
border is produced anteriorly in some individuals
(fig. 44) to form a sharp angle that marks the an-
terior limit of the insertion of the rhomboideus,
which is remarkable for the length of its insertion
line. In other individuals this angulation is miss-
ing. The scapular notch, which is at best poorly
developed in nearly all carnivores, is almost oblit-
erated in Ailuropoda and Ursus. The vertebral
border forms a smooth, gentle curve, with no clear
indication of the juncture of the coracoid and ver-
tebral borders (the anterior angle; median angle
of human anatomy). This blurring of the ante-
rior angle is characteristic of Carnivora. The pos-
terior extent of the vertebral border is determined
by the serratus ventralis; the rhomboids appar-
ently have no influence in determining the position
of the posterior angle. The axillary border, from
which the long triceps arises, is relatively straight
and clearly defined. Its juncture with the verte-
bral border (the posterior angle; inferior angle of
human anatomy) marks the juncture of the ser-
ratus ventralis and teres major muscles, and is
clearly defined.
In the Carnivora the ouiline, and hence the major
indices, of the scapula are determined by two muscle
groups related to the vertebral border: the rhomboids,
and the levator scapulae + serratus ventralis.
The lateral surface is slightly concave, and is
divided by the spine into the supraspinous and
infraspinous fossae. The infraspinous fossa con-
siderably exceeds the supraspinous in area, and
is relatively much larger than in the bears. This
increased size is due to an extension posteriorly of
the axillary border, as is shown by the angle formed
by the axillary border with the spine; this is 38-40
in Ailuropoda, 20-30 in Ursus. The floors of both
fossae are marked by vermiculate rugosities simi-
lar to those seen in the giant anteater, and there
is a nutrient foramen in each above the glenoid
cavity. The coracoid border of the supraspinous
fossa is sometimes raised and sometimes not, a
variation also found in bears. In some individuals
of Ailuropoda it is raised, so that the fossa is con-
cave in cross section, while in others it is depressed,
producing a prominent convexity in the fossa. The
axillary border of the infraspinous fossa is influ-
enced by the triceps longus, whose origin in the
bears and giant panda extends nearly or quite to
the posterior angle. This border is sinuous in Ailu-
ropoda, straight in the bears. The teres major
process lies behind the axillary border at the pos-
terior angle. The teres major muscle arises from
its posterior border. The lateral surface of this
process is excavated into the postscapular fossa,
from which the subscapularis minor muscle arises.
DAVIS: THE GIANT PANDA
91
M. acromiodelt.
M. biceps
M. subscapularis minor
Fig. 46. Ventral view of right scapula of Ailuropoda (left) and Ursus arctos (right).
In Ailuropoda the postscapular fossa is well
marked, but has been much reduced by the pos-
terior extension of the infraspinous fossa so that
it is much less conspicuous than in Ursus. The
postscapular fossa is continued toward the glenoid
cavity as a wide trough that extends the en-
tire length of the axillary border, separated from
the medial surface of the blade by a prominent
ridge, and from the lateral surface by the infe-
rior scapular spine. This trough (fig. 46), which
lodges the subscapularis minor muscle, is twisted
through 180.
The glenoid cavity is pear-shaped, with the apex
anteriorly, as it is in other carnivores and in mam-
mals generally. The notch that appears in the mar-
gin opposite the spine in certain carnivores {Canis,
Felis) is wanting in Ailuropoda and most other car-
nivores. In Ailuropoda the cavity is narrower (in-
dex
length X 100
breadth
= 645, mean of two specimens)
than in any other carnivore. It is also narrow in
bears (index 670, mean of 6 specimens), and gen-
erally narrower in arctoids than in aeluroids. The
cavity is shallow in both Ailuropoda and Ursus.
The neck is notable for its great anteroposterior
diameter, although this is slightly less than in Ur-
sus. The supraglenoid tuberosity, for the origin
of the tendon of the biceps, is a prominent scar
immediately above the anterior border of the gle-
noid cavity. Above and mesad of it is a slight
elevation, the coracoid process, bearing on its me-
dial surface a scar from which the tendon of the
coracobrachialis arises. The infraglenoid tuber-
osity, from which the anteriormost fibers of the
long triceps take tendinous origin, is much less
prominent than in Ursus. It is merely a rough-
ened triangular area above the lip of the glenoid
cavity that continues without interruption into
the axillary border.
92
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
M. infraspinatus
M. brachialis +
M. triceps lateralis "
M. triceps medialis
tcaput longum)
M. teres minor
M. acromiodelt
Crista deltoidea
M. brachialis
M. cephalohumer.
Crista pectoralis
M. ext. carpi radialis
longus et brevis
Crista epicondyltts lat.
M. anconaeus
M. ext. dig. comm. ct. lat
M. ext. carpi ulnaris
M. supraspin.
Tuber, majus
M. stemohumer. prof.
M. pect. superf.
M. brachialis
M. brachioradialis
M brachialis
Epicondylus lateralis
Fig. 47. Lateral view of right humerus of Ailuropoda.
The spine is slightly twisted, as it is also in bears,
reflecting the action of the deltoid and trapezius
muscles. The line formed by the crest of the spine
is convex posteriorly, in some individuals markedly
so (reflecting the pull of the acromiotrapezius?) .
The inferior part of the spine, just above the acro-
mion, is inclined slightly anteriorly, while the pos-
terior part is vertical or inclined slightly posteri-
orly. The lateral (free) border, again as in bears, is
squared in cross section. The spine is continued
ventrally into a heavy acromion process, which
functions in the origin of the acromiodeltoid and
levator scapulae ventralis muscles. The meta-
cromion, the process on the posterior border from
which the levator scapulae ventralis arises in most
carnivores, is not indicated in Ailuropoda and is
scarcely more prominent in Ursus. The lateral
surface of the acromion is flat and table-like in
both bears and panda.
In summary, the scapula of Ailuropoda agrees
with Ursus in all features that distinguish the bear
scapula from that of other carnivores. The most
notable difference between the panda and the bears
is the posterior expansion of the infraspinous fossa
in Ailuropoda, which seriously encroaches on but
does not obliterate the typically ursid postscapular
fossa. The infraspinous fossa is associated with
the infraspinous and long triceps muscles, which
DAVIS: THE GIANT PANDA
93
Tuber, minus
M. supi'aspin. j.
M. subscapularis
Tuber, majus
M. triceps medialis
(caput longum)
M. coracobrachialis brevis
M. pect. prof.-
Crista peclorali
M. teres major
M. latissimus dorsi
M. pect. supei f
M. triceps medialis
(caput intermedium)
M. eoracobrachialib longus
M. anconaeus
Fossa olecrani
M. flexor digitorum prof. (4)
M. flexor digitorum prof. (2)
Epicondylus medialis
M. pronator teres
M. flexor carpi radialis
M. flexor digitorum prof. (1)
M. palmaris longus
M. flexor carpi ulnaris
Fig. 48. Medial view of right humerus of Ailuropoda.
are involved in fixation and flexion of the shoulder
joint.
2. Humerus
The humerus in the Carnivora serves for the
origin or insertion of 28 muscles. Of these, 12 be-
long to the shoulder joint and 16 to the elbow joint
or lower arm and manus. The form of the humerus
is determined largely by these muscles.
In Ailuropoda the humerus is longer than the
radius, as it is in all arctoid carnivores except Pro-
cyon and most dogs. The mean ratios (length of
radius X 100/length of humerus) for various gen-
era are as follows:
Humeroradial
index *
N
Bassaricyon 1 72.7
Ailurus 3 74.7(72.1-77.8)
Ailuropoda 7 77.1 (74.7-79.7)
Bassariscus 4 79.0 (77.9-79.5)
Ursus (various species) 6 82.3 (78.3-85.8)
Nasua 2 85.5 (82.7-88.2)
Canis lupus 4 100.6 (98.1-102.9)
Procyon 4 100.9 (99.5-102.5)
* In generalized mammals the radius length is about 85
per cent of the humerus; this is true in such generalized ter-
restrial insectivores as Echinosorex, Erinaceus, and Soleno-
don. A. B. Howell (1944) states that in the generalized
condition the humerus and radius are about the same length,
but this is obviously not true for mammals at least. For
simple mechanical reasons the radius tends to lengthen with
cursorial locomotion, but reasons for shortening this bone
are not so clear. In man (European) the index is about 74.
94
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
The humerus of Ailuropoda (figs. 47, 48) does
not differ notably from that of other arctoid carni-
vores. It is slightly convex anteriorly. IVIuscle
scars are extremely prominent, and the area above
the olecranon fossa, where the anconeus muscle
arises, is marked by vermiculate rugosities similar
to those on the scapula. The angulation in the
profile at the inferior end of the deltoid ridge, char-
acteristic of bears, is wanting in the giant panda.
The head is offset posteriorly from the shaft; a
line drawn through the center of the shaft just
touches the anterior edge of the head. This is
similar to other arctoids, except Ursus in which
the head lies almost on top of the shaft.' The ar-
ticular surface greatly exceeds the opposing sur-
face on the scapula in area. The head in transverse
section forms a perfect arc of about 170, thus
nearly a semicircle. In frontal section it forms a
much smaller sector (about 65) of a circle nearly
twice the diameter, so that the head appears flat-
tened when viewed from the rear. In Ursus the
transverse section of the head is nearly identical
with that of Ailuropoda, but the frontal section
forms a slightly larger sector (78-93) of a circle
only slightly larger than that formed by the trans-
verse section. In other words, in the bears the
humeral head represents a part of a nearly perfect
hemisphere, while in Ailuropoda it tends toward
the almost cylindrical structure seen in such highly
cursorial forms as the horse.
The anatomical neck is scarcely indicated, ex-
cept posteriori}'. The tubercles are low and very
bear-like. The greater tubercle scarcely rises
above the level of the head. It is sharply defined
anteriorly, where it continues into the pectoral
ridge; its posterior boundary is almost obliterated
by the infraspinatus impression. The supraspi-
natus impression extends almost the entire length
of the dorsal lip of the greater tubercle. There are
several large nutrient foramina between the greater
tubercle and the head. The lesser tubercle is
prominent; the well-marked subscapularis impres-
sion covers practically its entire medial surface.
The intertubercular (bicipital) groove between
the two tubercles is wide and deep. In life it is
bridged over by the transverse humeral ligament
to form a canal. The groove lodges the tendon of
the biceps and transmits a branch of the internal
circumflex artery. There are a number of nutrient
foramina in the floor of the groove.
The shaft is triangular in cross section, because
of the several prominent crests. The single nutri-
ent canal that is prominent on the posterior surface
of the shaft in other arctoids is represented by sev-
' In other ursids {Thalarcios, Melursus, Helarctos) the
head is offset. Tremarctos is similar to Ursus.
eral minute foramina in Ailuropoda. The pec-
toral ridge (crista tuberculi majoris, BXA), on
the anteromedial surface, extends from the greater
tubercle nearly down to the distal end of the shaft.
It is a very prominent crest that provides inser-
tion for the superficial and deep pectoral muscles.
The deltoid ridge begins immediately below the
posterior end of the greater tubercle, on the pos-
terolateral surface of the shaft; near the middle of
the shaft it arches across the anterior surface of
the shaft and joins the pectoral ridge just below
the middle of the humerus. The deltoid ridge pro-
vides origin for the long head of the brachial mus-
cle and insertion for the cephalohumeral. Midway
between the pectoral and deltoid ridges there is
a third ridge, which marks the medial boundary
of the insertion of the cephalohumeral. Mesad of
the pectoral ridge, on the flat medial surface of the
shaft, is a prominent elongate scar 40-50 mm. long
that marks the insertion of the latissimus dorsi
and teres major.
Distally the shaft bears the tremendous wing-
like expansion of the lateral epicondylar ridge
on its posterolateral surface. This ridge extends
proximad nearly to the middle of the shaft. It
provides origin for the short head of the brachialis,
the brachioradialis, and the extensor carpi radi-
alis longus and brevis. These are all forearm flex-
ors, although the extensor carpi radialis is chiefly
an extensor of the hand. The lateral part of the
anconeus arises from its posterior face. This ridge
is well developed in all procyonids, in some of
which (e.g., Nasua) it is as prominent as in Ailu-
ropoda. It is about as well developed in bears as
in the giant panda. It is likewise present in mus-
telids, and is extremely well developed in bun'owers
such as Taxidea and Meles. It is scarcely indicated
in the cursorial dogs.
The distal end of the shaft is thinner antero-
posteriorly but wider than it is farther proximally;
it is relatively slightly wider and much thinner
than in bears. The trochlea ( = capitulum -f- troch-
lea of human anatomy) is almost identical with
that of Ursus, except that it is somewhat wider.
The trochlea is divided into lateral and medial
parts by a faint ridge that runs spirally postero-
laterally to terminate in the ridge bordering the
olecranon fossa. The lateral part of the trochlea,
with which the radius and a small part of the ulna
articulate, forms a semi-cylinder with only a very
faint anteroposterior groove. The medial part of
the trochlea, which forms the major ulnar articu-
lation, forms a trough-shaped spiral path extend-
ing posteriorly well into the olecranon fossa. This
spiral trough forces the ulna to shift medially
5 mm. or more as the elbow is flexed. The poste-
DAVIS: THE GIANT PANDA
95
rior part of this trough has an extremely prominent
external lip on which the articular surface faces
medially. The coronoid fossa, above the troch-
lea anteriorly, is entirely wanting, as it is also in
bears. The olecranon fossa, above the trochlea
posteriorly, is deep and relatively wider than in
Ursus.
ratio, length pelvis/length radius is 130.3 (126.8-
132.7) in Ailuropoda, 110.3 (107.3-118.4) in Ursus,
100.9 (95.5-103.3) in Procyon, 108.2-108.8 in Ailu-
rus, 110.9 (105.3-113.9) in Bassariscus, and 78.4
(76.3-80.1) in Canis. The significance of the re-
duced radius length in Ailuropoda is discussed be-
low (p. 102). In both panda and bears the radius
Ailuropoda
Ursus
Canis
Procyon
Fig. 49. Distal ends of humeri of Ailuropoda, Ursus americanus, Canis lupus, and Procyon loior.
The medial epicondyle is more prominent and
more vertically compi'essed than in Ursus. It pro-
vides origin for the pronator teres, flexor carpi ra-
dialis, flexor digitorum profundus, palmaris longus,
and flexor carpi ulnaris. These are all flexors of the
hand, except the pronator teres, which pronates
the forearm. The entepicondylar foramen,
which transmits the median nerve and median
artery, was present in all specimens of Ailuropoda
examined. This foramen is absent in the Ursidae
(except Tremarctos ornatus) and Canidae, present
in the Procyonidae, in Ailurus, and in most Mus-
telidae. Its presence in Ailuropoda and Tremarc-
tos is probably a secondary condition correlated
with the large size of the epicondyle in these two
genera.
The lateral epicondyle is less prominent than
in Ursus, and is considerably narrower. It pro-
vides origin for the extensor digitorum communis
and lateralis and the extensor carpi ulnaris. These
are all extensors of the manus, although the ex-
tensor carpi ulnaris chiefly abducts the hand ulnar-
ward. It has no direct genetic basis, and in this
instance cannot be used as a "character."
The humerus of Ailuropoda is so similar to that
of the bears, especially to such forms as Tremarctos
and Melursus, that Lydekker's statement (1901)
to the contrary is almost incomprehensible.
3. Ulna and Radius
The ulna is slightly heavier than in a bear of
comparable size, while the radius is slightly more
slender. The radius is shorter in relation to pelvic
length than in any other carnivore measured. The
lies almost entirely laterad of the ulna at the elbow
joint. The radius is slightly more dorsal in Pro-
cyon and Ailurus, and in the narrow elbow joint
of the cursorial dogs it lies almost in front of the
ulna.
The form of the ulna is very similar to that of
Ursus. The olecranon, measured from the center
of the semilunar notch, averages 14 per cent of the
length of the humerus;' this is likewise true for
Ursus, Procyon, and Ailurus, while in Canis it is
longer (19 per cent). The olecranon, which pro-
vides insertion for the triceps complex and the
flexor carpi ulnaris, is a heavy knob-like extension
of the ulna, bent slightly medially. The medial
surface is concave and is devoid of muscle attach-
ments; the lateral surface provides attachment for
parts of the triceps and anconeus. Anteriorly the
olecranon forms the prominent anconeal process,
which interlocks with the olecranon fossa of the
humerus and forms the posterior part of the semi-
lunar notch.
The semilunar notch, bounded anteriorly by
the coronoid process and posteriorly by the an-
coneal process, is almost a perfect semicircle in
profile. It is arched in cross section, lacking the
median guiding ridge seen in dogs. The anconeal
process has an extensive external face that rides
against the external lip on the posterior part of
the trochlea, and the coronoid process an internal
face that rides against the inner wall of the troch-
lear groove. This arrangement effectively locks
the elbow joint and prevents any medial shifting
' Calculation as percentage of ulna length gives mislead-
ing values in forms with elongated fore arm, such as Procyon
and Canis.
96
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
M. anconaeus
Incimira seiniliotari
Proc. coroiioideus.
M. brachialis
M. biceps
M. supinator
M. flexor digitorum prof. 3
M. pronator teres
M. pronator quadratus
M. triceps
Olecra}ion
M. flexor carpi ulnaris
M. flexor digitorum prof. 5
M. pronator quadratus
Proc. .^Iiiloidviis
Fig. 50. Right ulna and radius of Ailuropoda, posteromedial view.
of the distal end of the ulna; there is no such pro-
tection against lateral shifting.
The radial notch is a shallow depression on the
lateral side of and immediately below the coronoid
process, in which the head of the radius rotates.
The shaft tapers gradually toward the distal
end. It is slightly bowed, with the convexity out-
ward. The bone is wider anteroposteriorly than
it is from side to side. Immediately below the
coronoid process, on the anterior surface of the
bone, there is a prominent ovoid depression that
marks the insertion of the brachialis tendon. In
most specimens a wide rugose ridge along the mid-
dle third of the lateral surface of the shaft marks
the attachment of the interosseous ligament.
The distal end of the ulna is slightly expanded.
Dorsally it bears a circular, much-rounded artic-
ular facet for the radius. Beyond this the shaft
is continued into the short peg-like styliform
process, which bears a rounded facet for the cu-
boid and pisiform on its anteromedial surface.
The radius is curved in both planes; it is slightly
convex anteriorly, and forms a long S-curve in the
lateral plane. This complex curvature of the ra-
dius is seen to some degree in all Carnivora except
the cursorial dogs.
The capitulum of the radius is set off by a very
distinct neck. It is an elliptical disk, the long
diameter running from anterolateral to postero-
medial. The ratio of long to short diameter is
DAVIS: THE GIANT PANDA
97
about 10 : 7, and this ratio is about the same as
in Ursus. In burrowing forms (Taxidea, Meles)
the capitulum is even more ovate, whereas in ar-
M. triceps
cumference of the head; the medial one-fourth,
where the capitular eminence is situated, has no
articular surface.
M. anconaeus
M. abductor poll, longus
M. ext. indicus proprius
M. ext. dig. lat.
M. ext. carpi ulnaris
Emiiieiilia capllulorum
M. abductor poll, longus
M. supinator
M. pronator teres
M. abductor poll, longus
M. ext. dig. comm.
M. ext. carpi radialis longus
M. ext. carpi radialis brevis
Fig. 51. Right ulna and radius of Ailuropoda, anterolateral view.
boreal forms {Procyon, Nasua, Polos) it is more
nearly circular.
The capitular depression, which articulates with
the lateral part of the trochlea of the humerus, is
very shallow. On its anteromedial circumference
it bears a low elevation, the capitular eminence,
that forms the anterior lip of the radiohumeral
articulation in all positions of the radius, and acts
as a stop that limits the excursion of rotatory
movements of the radius. The articular circum-
ference, which articulates with the radial notch of
the ulna, is not continuous around the entire cir-
The shaft of the radius is triangular in cross sec-
tion, the base of the triangle forming the flat ven-
tral surface of the bone. The radial tuberosity, for
the insertion of the biceps tendon, is on the ventro-
medial surface immediately below the neck. Oppo-
site this, on the anterior aspect, is a scar marking
the attachment of the lateral collateral ligament.
The interosseous crest, for the attachment of the
interosseous ligament, begins below the radial tu-
berosity as a wide, roughened scar for the heavy
proximal part of the ligament. A little above the
middle of the bone it changes abruptly into a
ridge-like crest.
Sesamoid, rad.
Trapezoid
Trapezium
Scapholunatum
Magnum
Unciforme
Cuneiforme
Pisiforme
Fig. 52. Right carpus and metacarpus of Ailuropoda, dorsal view.
Fig. 53. Right carpus and metacarpus of Ailuropoda, ventral view.
98
DAVIS: THE GIANT PANDA
99
The distal end of the radius is expanded and
bears two articular surfaces, the large concave car-
pal surface for articulation with the scapholunar,
and laterally the small flat ulnar notch for articu-
lation with the ulna. The carpal surface is nar-
rower from side to side but wider anteroposteriorly
than in Ursus, thus providing a less trough-like
articulation for the carpus. The prominent saddle
shape of the articular area on the styloid process
that is seen in Ursus is scarcely indicated in Ailu-
ropoda. Also the medial end of the articular sur-
face is in Ailuropoda deflected proximally toward
the ulnar notch. The styloid process is a blunt
projection on the medial side; a deep furrow on its
dorsolateral surface lodges the tendon of the ab-
ductor poUicis longus. Just laterad of this, on
the dorsal surface of the styloid process, is a shal-
low furrow for the tendon of the extensor carpi
radialis longus, separated by a ridge from the fur-
row for the extensor carpi radialis brevis. Another
shallow furrow near the lateral border lodges the
tendon of the extensor digitorum communis.
4. Carpus
The carpus (figs. 52, 53) is very similar to that of
bears, except for the tremendous development of
the radial sesamoid and the modifications of the
scapholunar associated therewith. The carpus-fore-
arm articulation is largely between the scapholunar
and the radius, which form an almost ball-and-
socket joint permitting very extensive excursion.
The styloid process of the ulna, as in bears and
procyonids, is lodged in a widely open notch
formed by the cuneiform and pisiform.
The carpus is dominated by the scapholunar.
This bone greatly exceeds any of the other carpals
in size, and articulates with all the other carpal
bones except the pisiform, and with the radius and
the radial sesamoid. The articular surface for the
radius occupies almost the entire dorsal and poste-
rior surfaces of the bone, forming an ovate articula-
tion that in some individuals is in contact anteriorly
with the articular surface for the trapezium. This
is more extensive than in any other carnivore, al-
though in Ailurus and Potos it is closely approached.
In Ursus the lateral part of this surface has a
dimple-like depression, to receive the saddle on the
distal end of the radius; this depression is com-
pletely wanting in Ailuropoda and in Ailurus and
Potos. The anteromedial end of the bone is pro-
duced into a stout hook-like process, directed ven-
trally, that bears a prominent articular surface for
the radial sesamoid on its anteromedial surface.
This articular surface is an elongate oval, its long
axis vertical, and is convex in both planes. The
anterior surface of the scapholunar bears three ir-
regular shallow excavations for the trapezium.
trapezoid, and magnum, and the lateral surface
bears articular facets for the magnum and unci-
form.
The cuneiform is very similar to the corre-
sponding bone in Ursus, but relatively slightly
larger. It articulates with the scapholunar, the
pisiform, and the unciform.
The pisiform is, next to the scapholunar, the
largest bone in the carpus, and is very similar to
the corresponding bone in Ursus. It articulates
with the cuneiform, forming with it a shallow V-
shaped notch dorsolaterally, in which the styliform
process of the ulna articulates. The bone extends
posteriorly, ventrally, and slightly laterally from
the carpus, its expanded tip embedded in a large
fibro-fatty pad that underlies the lateral carpal
pad. Five muscles and five ligaments attach to
the bone. The tendon of the flexor carpi ulnaris
attaches to the posterior surface, the opponens and
abductor digiti quinti and palmaris brevis to the
anterior surface, and the flexor digiti quinti to
the inner border. A prominent scar near the tip
on the anteromedial surface marks the attachment
of the transverse carpal ligament, and another scar
on this surface proximally marks the attachment
of the pisometacarpal ligament.
In the distal row the trapezium and trapezoid
are very small, articulating distally with meta-
carpals 1 and 2 respectively. The magnum is
larger, and articulates with metacarpal 3. The
unciform bears metacarpals 4 and 5.
The radial sesamoid (fig. 54) is the most ex-
traordinary bone in the fore foot. It is about
35 mm. in length, and lies in line with the meta-
carpals, closely resembling a sixth metacarpal on
the medial border of the hand. It underlies the
accessory lobe of the carpal pad. The bone is com-
pressed from side to side, measuring about 15 mm.
in height by only 6 or 7 mm. in thickness. The
distal end hooks sharply inward toward the first
metacarpal. The radial sesamoid articulates ex-
tensively with the enlarged medial process of the
scapholunar, and is in contact with the medial
border of the first metacarpal. The articular sur-
face for the scapholunar is ovate with the long
axis dorsoventral, and is concave both laterally
and dorsoventrally. The contact surface with the
first metacarpal is dorsomedial, and is not cartilage
covered. A large depression on the outer surface
of the radial sesamoid near the base marks the
attachment of the tendon of the abductor pollicis
longus. The abductor pollicis brevis and opponens
pollicis arise from its medial surface.
A sizable radial sesamoid articulating with the
scapholunar is present in all the other arctoid car-
nivores, and a corresponding bone exists in many
100
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
(^
B
d
Ailuropoda Tremarctm Ursus Ailurus Procy<m
Fig. 54. Relative sizes of (A) right radial sesamoid, and (B) right tibial sesamoid in representative carnivores.
other mammals. In no other arctoid does it ap-
proach the proportions seen in Ailuropoda, how-
ever. In Bassariscus, Procyon, and Nasua it is a
small bony nodule, and in Procyon at least it lies
beneath the tendon of the long abductor. The
radial sesamoid is also relatively small in Ursus
but provides attachment for a part of the long
abductor and opponens (fig. 54). The bone is rel-
atively larger in Ailurus, and the tendon of the
long abductor inserts into it exclusively, as in Ailu-
ropoda (see also p. 180).
Comparison of the relative sizes of the radial ses-
amoid and the tibial sesamoid, the corresponding
bone in the hind foot, is very suggestive (fig. 54) .
The tibial sesamoid has no function corresponding
to that of the radial sesamoid, yet as is evident
from the figure it undergoes a corresponding in-
crease in size. This indicates a genuine serial ho-
mology between these two bones, with a common
genetic control of the size factor at least, i.e. that
the radial and tibial sesamoids represent a morpho-
genetic field despite their physical remoteness from
one another.
5. Manus
The metacarpals are short and stout, relatively
considerably shorter than in a bear of comparable
size. As in other arctoids (except Canis), the fifth
is heavier than the other four. Length relations
are the same as in Ursus, although the differences
are more exaggerated; the fourth is the longest,
followed in order by the fifth, third, second, and
first. Ailurus is similar, while in Procyon, Nasua,
and Bassariscus the third metacarpal is longest.
The distal articular surface of the metacarpals
is narrower than in Ursus, especially dorsally, and
the median ridge is more prominent. A conspicu-
ous scar on the radial side of the second meta-
cai-pal, just proximad of the middle, marks the
insertion on the tendon of the extensor carpi radi-
alis longus, and a similar scar, situated farther
proximad on the third metacarpal, the insertion
of the extensor carpi radialis brevis.
The phalanges are similar to those of Ursus,
except that they are somewhat stouter. Those of
the proximal row are all slightly convex dorsally,
more so than in Ursus. The bones of the middle
row are very similar to the corresponding bones in
bears. On the distal articular surface the median
furrow is slightly deeper than in Ursus, corre-
sponding with the more prominent median ridge
on the terminal phalanges. In the terminal pha-
langes the core of the claw is higher vertically than
in Ursus; the dorsal margin is more curved than
in bears, the ventral margin less so.
A pair of sesamoid bones is present beneath
the metacarpophalangeal articulation of each digit
There are 10 in all. This is typical for all arctoid
carnivores except the Canidae, in which the first
digit has only one.
B. Review of the Fore Leg
The bones of the fore leg of Ailuropoda agree
closely with those of Ursus in all essential respects.
Claenodon corrugatus
Polos flovus
Ursus arclos
Ailuropoda melonoleuco
Fig. 55. Right manus of representative carnivores, dorsal view. (Claenodon from AMNH 16543.)
101
102
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
The differences may be examined briefly for evi-
dence of their significance in interpreting the mor-
phology of the giant panda.
All the large bones in the panda exhibit more
prominent modeling, and this is broadly adaptive.
Details of modeling, however, are determined by
surrounding muscles rather than genetically (p.
147), and this difference therefore merely reflects
the more powerful musculature of this animal.
The presence of an entepicondylar foramen in
Ailuropoda contrasts with its absence in all bears
except Tremardos. This likewise appears to be
merely a secondary result of enlarged muscles and
their bony attachments (see Stromer, 1902). The
presence or absence of this variable structure,
which has aroused so much discussion in the litera-
ture, probably has no direct genetic basis.
There are considerable differences between the
giant panda and bears in the form of several ar-
ticular surfaces. The shoulder articulation allows
a greater range of lateral movement in bears, which
cannot be correlated with any known difference in
habits or behavior. There is no appreciable dif-
ference in the elbow. The articulation between
forearm and wi'ist permits notably gi'eater dorso-
ventral excursion in the giant panda than in bears,
and this is very obviously coirelated with the
greater maneuverability of the hand in the giant
panda. Articulations reflect, rather than deter-
mine, range of movement in a joint (p. 145), how-
ever, and here again no genetic control can be
postulated for adaptive differences in the skeleton.
As shown by the radiohumeral index, the fore-
arm is significantly shorter than the upper arm in
the giant panda, relatively shorter than in Ursus
where it is near the norm for generalized mammals.
Little is known of the functional significance of
shortened forearm, and even less of mechanisms
controlling the lengths of long bones. It has been
concluded (p. 38) that the limb proportions in
Ailuropoda do not reflect mechanical requirements.
The enlarged, maneuverable radial sesamoid in
the giant panda is the most notable departure from
the ursid pattern. This remarkable mechanism is
unquestionably a direct product of natural selec-
tion. The correlated enlargement of the tibial
sesamoid, together with a consideration of the
muscles and ligaments functionally associated with
the radial sesamoid (p. 183), clearly indicate that
simple hypertrophy of the bone was all that was
required to produce the whole mechanism. The
genetic mechanism underlying such hypertrophy
may be, and indeed probably is, quite simple. A
further, but relatively minor, polishing effect of
natural selection is evident in the detailed model-
ing of the bone.
Thus of the appreciable morphological differ-
ences in the bones of the fore leg of the giant panda
and the bears, most are seen to be physiological
adjustments to primary differences in the muscu-
lature. Such adjustments are not intrinsic to the
bones, and therefore not gene controlled. Minor
details, such as slight differences in individual car-
pal bones and the shape of the terminal phalanges,
reflect at most minor polishing effects of natural
selection. Only two adaptive features, the relative
shortness of the forearm and the remodeling of the
radial sesamoid, appear to result directly from nat-
ural selection on the bones themselves.
VII. THE HIND LEG
In quadrupeds the hind leg during locomotion
is more important than the fore leg as an organ of
propulsion. The mass of the musculature of the
hind quarters accordingly exceeds that of the fore
quarters. In most mammals the hind leg has far
less varied functions than the fore leg; it is pri-
marily an organ of support and propulsion. The
forces acting on the pelvis and hind limb are there-
fore usually less varied and less complex than those
on the fore leg. In the giant panda the fore leg
has diverged far more from the normal quadru-
pedal function than the hind leg, and this is only
slightly less true of the bears and procyonids.
Like the fore leg, the hind leg of carnivores is
basically designed for cursorial locomotion.
A. Bones of the Hind Leg
1 . Pelvis
The pelvis, like the scapula, is molded primarily
by muscular action. Thrust from the ground is
transmitted from the femur to the sacrum through
the body of the ilium, and this, together with the
acetabulum and the iliosacral union, reflects chiefly
non-muscular forces.
The pelvis of the giant panda differs remarkably
from that of any other arctoid. The ilia lie in the
frontal, rather than the sagittal plane, the pubis
is shortened, and the length of the sacroiliac union
is increased (see p. 82). The pelvis most closely
resembles that of burrowing forms such as Taxidea
and especially Mellivora; actually it is most sim-
ilar to the pelvis of the burrowing marsupial Vom-
batus. This extraordinary convergence in animals
with dissimilar habits is understandable when the
forces operating on the pelvis are analyzed (p. 109).
Table 11 gives measurements and proportions
of the pelvis of a number of arctoid carnivores.
From these figures it is evident that certain pro-
portions remain relatively constant, regardless of
the habits of the animal, while others vary con-
DAVIS: THE GIANT PANDA
Table 11. MEASUREMENTS AND INDEXES OF PELVIS IN CARNIVORES
103
B
D
Preace- Width
Length tabular Iliac iliac
pelvis length breadth crest
Ailuropoda
31128 272 168 230 75
110452 290 179 268
110454 280 168 245
259027 292 193 265 88
259401 268 166 239
259403 282 176 257 82
259402 290 180 260
258425 266 170 240
MEANS:
Vrsus amer.
18864 205 130 194 86
44725 238 148 206 95
Ursus arclos
43744 271 175 255 90
47419 302 196 282 114
Ursus gyas
27268 390 215 401 167
63803 312 181 320 131
MEANS:
Ailurus fulgens
65803 90 57 50 23
44875 74 47 41 18
Procyon lotor
49895 114 69.5 72 29
49227 107 64 72 26
49057 98 57 68.5 26
47386 103 60 77 29
Canis lupus
51772 197 114 108 65
54015 177 112 117 57
21207 184 112 107 63
Mellivora
43298 89 53 80 22
Vombatus
49085 185 119 168 55
E F G
Width
Length across Width
sym- dorsal across
physis acetab. ischia
INDEXES
BxlOO CXIOO DXlOO EXIOO FxlOO GXlOO
A A A A A A
51
54
54
54
50
51
52
45
21
16
65
58
59
18
31
133
148
135
150
129
145
140
135
145
160
156
166
148
177
166
155
62
62
60
66
62
62
62
64
93
88
91
89
91
90
90
28
30
29
18.4
18.6
18.2
19.0
17.9
18.7
19.2
18.4
46.5 45
38.5 36.5
26 58
26.5 56.5
26 50
28.5 59
45
100
61
62
53
59
91 141
85.5 123
88 133
50
121
61.5
63
64
61
60
58
58
58
63
61
59
65
95.8
56
55
63
67
70
75
55
66
58
90
91
39.7 37.5
25
24
25
24
27
28
33
32
34
25
30
23
22
23
25
27
28
33
33
32
20
17
49
51
48
51
48
51
48
53
51.5
52
52
51
53
51
57
46
48
48
51
54
53
55
56
57
55
63
57
58
62.5
89.6
29
18.6
49.9
56.7
78
93
118
130
133
133
64
62
95
87
42
40
38
39
53
55
65
56
95
115
140
146
171
168
65
65
94
93
33
38
35
38
52
48
63
56
155
113
199
155
237
186
55
58
103
103
43
42
39
36
51
50
61
60
60.2
50
52
54
58
54
57
72
70
72
56
65
siderably. Using total length of pelvis as a base,
the position of the acetabulum (indicated by pre-
acetabular length, B) varies little. This is also
true of the distance between acetabula (F), which
is the functional diameter of the pelvis. On the
other hand, breadth across the ilia (C), breadth
across the ischia (G), and length of symphysis (E)
vary greatly with habits. This is also true of the
slope of the wings of the ilia and of the descending
ramus of the ischium with respect to the frontal
plane.
The pelvis is very short in Ailuropoda; length
pelvis/length Th 10-12' =33 and 35 in two indi-
viduals. The pelvis is also short in Ursus and the
badgers.
Morphology. The pelvis is rectangular in dor-
sal outline (fig. 56), depressed in lateral view (fig.
57). In posterior view it is U-shaped rather than
'See page 35.
V-shaped as in Ursus. In Ailuropoda the greatest
length of pelvis is about 40 per cent of the length
of the vertebral column, compared with about 29
per cent in Ursus americanus and 31 per cent in
Procyon lotor. This merely reflects the shortened
column in the panda, however; measured against
three thoracic vertebrae the pelvic length is com-
parable to that of Ursus.
In all specimens examined the sacro-iliac union
is more or less fused dorsally but open ventrally.
This is likewise true in Ursus, and contrasts with
the open articulation in other arctoids.
The ilium is composed of a remarkably narrow,
almost parallel-sided ala, and a short heavy corpus.
The ala is widest across the iliac crest, which is of
normal width; behind the anterior superior iliac
spine the inferior border is deeply excised and the
diameter of the ilium correspondingly narrowed.
The anterior superior iliac spine, which gives
origin to the sartorius and tensor fasciae latae
M. obliquus abdom. intonus
Ineimira isehiad. major
M. pyriformis
M. glutaeus prof.
M. rectus femoris
Tuber isehiacl.
M. gem. post.
Lig. $acTOluberosum
M. glutaeus supof.
M. biceps
M. semitendinosus
M. semimembranosus
Arau ischiad.
Fig. 56. Male pelvis of Ailuropoda, dorsal view. (Inset, A, pelvis of Ursus arctos.)
104
i
DAVIS: THE GIANT PANDA
105
M. pyriformis
Incisura isrhiad. major
Incisum iscliiad. minor
M. gem. post.
Lig. sfKrotubi^rosu
M. glutaeus superf.
Tuber itn-hlad.
M. semitendinosus
M. biceps
M. sartorius
Spiiio iUaca ant. sup.
Lima glutaea inf.
M. glutaeus prof.
M. adductor
Ramus descendens
ossis ischii
Ramu.t acetabularis ossis pubis
- M. obturator extemus
>M. adductor
sM. gracilis
M. rectus abdominis
Fig. 57. Male pelvis of Ailuropoda, lateral view. (Inset, A, pelvis of Ursus arcios.)
muscles and the anterior end of the inguinal liga-
ment, is thick and heavy. It lies farther anterior
than in Ursus, and the iliac crest is correspond-
ingly shorter and less curved. The posterior supe-
rior iliac spine is also relatively heavy. The
anterior and posterior inferior iliac spines are not
even indicated. The dorsolateral surface of the
ilium, which provides origin for the middle and
deep gluteals, is a shallow elongated trough, the
gluteal fossa. It is devoid of surface modeling ex-
cept for a faint vermiculation near the iliac crest.
The area of the gluteal fossa is about 5700 and
7500 mm." in two specimens of Ailuropoda, 7200
mm.- in a specimen of Ursus americanus, and
11,900 mm.- in a specimen of Ursus arctos.' The
ventro-medial surface of the ilium (fig. 58), which
provides origin for the iliacus, quadratus lumbo-
rum, and sacrospinalis muscles, is slightly convex
along both its axes. A faint longitudinal ridge,
not always evident, divides the surface into a lat-
eral iliac area and a medial sacrospinal area; this
is called the pubic border by Flower, Straus, and
See p. 43 for method used in measuring areas on bones.
other anatomists. A low but prominent elevation
near the middle of the ridge is associated with the
origin of the sacrospinalis. A large foramen-like
opening at the posterior end of the ridge, and lying
in the sacroiliac articulation, is filled with fat and
connective tissue in life; it is present but is usually
less foramen-like in Ursus, and apparently repre-
sents the separation between the dorsal and ven-
tral elements of the embryonic transverse processes
of the first sacral.
The corpus is short and heavy, only slightly lat-
erally compressed as in Ursus. Its superior border
bounds the greater sciatic notch, which has been
crowded posteriorly by the posterior extension
of the sacroiliac union. The inferior surface is
rounded, without crests or ridges. The iliopectin-
eal eminence is a low elevation, much less promi-
nent than in Ursus, on the inferior surface just
anterior to the acetabulum. The inferior gluteal
line, separating the gluteal and iliac surfaces of
the ilium, is scarcely indicated on the corpus. Im-
mediately in front of the acetabulum it passes into
the iliopubic eminence, which is likewise much less
106
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
M. iliocostalis
. transversus abdominis
M. sartorius
M. pectineus
M. rectus femoris
Fig. 58. Male pelvis of Ailuropoda, ventral view.
prominent than in Ursus; it marks the attachment
of the rectus femoris.
The articular surface of the ilium (fig. 59), which
articulates with the auricular surface of the sa-
crum, resembles that of Ursus but is relatively
longer and narrower. It is an elongate horseshoe,
open anteriorly, with a very irregular surface, the
irregularities interlocking closely with correspond-
ing irregularities on the sacrum. The narrow space
enclosed by the horseshoe is filled with fibrocarti-
lage. The extensive articulation, intimate dove-
tailing, and partial fusion of the sacroiliac joint
contrast sharply with the relatively smooth and
much smaller auricular surface of other arctoids.
The pubis is the most delicate bone in the pel-
vis. It is more lightly built than in Ursus, and
much more so than in the cursorial dogs. The
corpus, which forms the ventral part of the ace-
tabulum, is the heaviest part of the bone. The
acetabular ramus is very slender and elongate; it
had been fractured bilaterally in one specimen ex-
amined. The reduction in the length of the sym-
physis has taken place anteriorly, and the angle
formed by the acetabular ramus with the symphy-
DAVIS: THE GIANT PANDA
107
Canis lupus lycaon
Procyon lotor
Ursus arctos
AiluropodQ melonoleuca
Fig. 59. Articular surface of left ilium in representative arctoid carnivores.
sis in the sagittal plane is about 45 instead of 25-
35 as in Ursus, and the acetabular ramus is cor-
respondingly longer. The length of the symphyseal
ramus cannot be determined, since no available
specimen is young enough to show the suture be-
tween the pubis and the ischium. It is obviously
very short, however, and is relatively much wider
than in Ursus. The external surface of the sym-
physeal ramus provides origin for the anterior
parts of the gracilis, adductor, and external ob-
turator muscles; the internal surface provides ori-
gin for the anterior part of the internal obturator.
The ischium is not directly involved in the sup-
port function of the pelvis, except during sitting;
it functions chiefly as anchorage for the posterior
thigh muscles. The ischium does not differ much
from that of Ursus or Procyon. It is composed of
a stout acetabular ramus and a more slender de-
scending ramus (tabula ischiadica of veterinary
anatomy), and a heavy symphyseal ramus. The
acetabular ramus is relatively shorter than in Ur-
sus, and is ovate in cross section. Its shaft is almost
free of muscle attachments; only the tiny gemelli
arise from it. The sciatic spine, which separates
the greater and lesser sciatic notches, is a short
prominent transverse ridge as in Ursus. A small
scar immediately anterior to the spine marks the
attachment of the anterior gemellus, and immedi-
ately behind the spine there is a smooth area, cov-
ered with cartilage in life, over which the internal
obturator rides. The saddle-shaped area between
the sciatic spine and the ischial tuberosity is the
lesser sciatic notch. It is converted into a fora-
men by the sacrotuberous ligament, and transmits
the distal end of the internal obturator muscle and
various vessels and nerves.
The ischial tuberosity is by far the most promi-
nent feature of the ischium, and most of the mus-
cles attaching to the ischium are inserted on or
near it. The tuberosity is knob-like, about 35 mm.
in diameter, with a much roughened posterior sur-
face It has no inferior boundary, but continues
directly into the roughened swollen posterior edge
of the descending ramus, which narrows gradually
as it descends and terminates abruptly about 40
mm. above the symphysis. The muscle attach-
108
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
ments are around the periphery of the tuberosity;
the major part of its roughened posterior face Hes
directly beneath the skin. The tuberosity is simi-
lar, but more sharply bounded inferiorly, in Ursus.
The lower third of the descending ramus, below
the swollen area just described, is much the slen-
derest part of the ischium ; it is no heavier than the
acetabular ramus of the pubis. It provides attach-
ment for the posterior ends of the adductor and
gracilis externally, and for the internal obturator
internally. The descending ramus forms an angle
of about 55 with the sagittal plane. This angle
is similar in other arctoids examined except in
Canis, in which it is only about 20 (fig. 61).
The symphyseal ramus, forming the posterior
part of the symphysis pelvis, is broad and thick;
the minimum transverse diameter of the entire
symphysis (from obturator foramen to obturator
foramen) is 40-50 mm. in Ailuropoda, whereas in
a bear of comparable size it is 20-30 mm. In dor-
sal view the sciatic arch, which is often non-existent
in bears, is relatively deep.
The acetabulum, composed of a horseshoe-
shaped articular portion embracing a non-articu-
lar fossa, differs little from that of Ursus and other
arctoids. It looks slightly more laterally, forming
an angle with the vertical of 11 and 14, respec-
tively, in two individuals, 15 in three specimens
of Ursus. The acetabulum looks more ventrally
in the cursorial wolf, forming an angle of 29 (26-
31) in three specimens of Canis lupus.
The acetabulum is situated farther dorsad in
Ailuropoda than in Ursus, its dorsal border lying
well above the margin of the greater sciatic notch.
The entire rim of the acetabulum is extremely
heavy. The acetabular notch is almost twice as
wide as in a bear of comparable size; the anterior
boundary of the notch has been shifted forward
to produce this increased width. The acetabular
fossa is also relatively wider, and has increased its
diameter by encroaching on the anterior arm of
the articular portion, which accordingly is nar-
rower than in Ursus.
The obturator foramen is triangular in out-
line, rather than ovate as in Ursus.
Architecture and Mechanics. The mam-
malian pelvis is an extraordinarily complex struc-
ture, subject to varied and often subtle forces.
Moreover, it has had a long history, and treating
the mammalian pelvis as if it were engineered de
novo leads to difficulties and often even to absurdi-
ties. Mijsberg's work (1920) was one of the first
attempts to analyze the architecture and mechanics
of the non-human mammalian pelvis. Other such
studies have been made by Elftman (1929), Rey-
nolds (1931), Kleinschmidt (1948), and Maynard
Smith and Savage (1956).
The mammalian pelvis serves three dissimilar
purposes: (1) to provide support; to transmit thrust
from the legs to the vertebral column, and from
the column to the legs; (2) to provide attachment
surfaces and lever arms for hip and thigh muscles;
and (3) to transmit the terminal parts of the diges-
tive and urogenital canals, especially important
being the birth canal. Each of these has partici-
pated in molding the pelvis, but the basic archi-
tecture was largely determined by the support
function. Elftman believed that the pelvis is
"roughly modeled so as to fit the viscera and with
finer detail so developed as to provide optimum
support against gravity and leverage for loco-
motion."
As a supporting structure the pelvis is a complex
system of arches and levers designed to provide
strength and elasticity. Absorption of shock re-
sulting from impact between the feet and the
ground seems to have been a major factor in the
design of limbs and girdles in mammals. The ar-
chitecture of the mammalian pelvis, which is far
less rigid than that of their reptilian ancestors, is
otherwise unintelligible.
In the frontal plane (fig. 60, B) the pelvis is com-
posed of two round arches meeting at the acetab-
ular a heavy dorsal arch composed of the two ilia
and the sacrum, and a much lighter ventral ilio-
pubic arch. Only the dorsal arch is directly in-
volved in the support function of the pelvis; the
ventral arch is concerned with the structural sta-
bility of the pelvis. The dorsal arch is loaded both
from above (weight of body, W) and from below
(upward thrust of legs, T). In addition to bend-
ing and shearing stresses, the loaded arch develops
horizontal thrust which reaches a maximum at the
base (the acetabula. A, A) whether loading is from
above or below. The sole function of the iliopubic
arch, aside from providing a base for muscle at-
tachment, appears to be as a bottom tie for the
dorsal arch, to counteract this horizontal thrust.
Viewed from the side (fig. 60, D) the pelvis is
not a simple arch as it is in reptiles. The acetab-
ulum lies well behind the sacroiliac articulation,
and upward thrust through the acetabulum is
translated into a vertical rotational force around
the sacroiliac articulation as a center; the coxa is
cantilevered to the sacrum. The sacroiliac articu-
lation is not normally fused in quadrupeds, but it
is practically immovably fixed by the sacroiliac
ligaments, often augmented by interlocking den-
ticulations on the two articular surfaces. Thus,
under loading, shearing forces are developed along
the neck of the ilium the axis connecting acetab-
A. Alligotor Tronsverse iliosocrol orch
of quadrupedal mammals CB).
similar to orch
Aliigotor Thrust T through acetabulum is transmitted
directly to socroilioc joint 0^. The iliosocrol orch
fufKtions OS simple orch ,
H-<
>H
B. Conis, Upword thrust T, T' through ocetobulo is resolved
in transverse iliosocrol orch. This orch is also loaded
from obove by the weight of the body, Vi_. Horizontal
thfust, H, H, developed in the tronsverse orch by both T_
and W, is counteracted by the ventral iliopubic orch oct-
ing OS a tie.
Conis . Thrust T through acetabulum is translated into
rototionol force R oround socroilioc joint os o cen-
ter. This produces o shear along the oxts 0-A, as
indicated by x - xv Horizonol thrust H is developed dur-
ing locomotion.
Conis. Upword thrust T is tronsmitted
directly to vertebral column through ilium
and sacroiliac joint. A shear is pro-
duced at ttw socroilioc joint and com-
pression in the reck of ttw ilium. The
socroilioc orch functions as o simple
orch.
Fig. 60. Forces acting on the pelvis in quadrupeds. A, transverse arch in a reptile, anterior view; B, transverse arch in
a mammal, anterior view; C, transverse arch in a reptile, lateral view; D, cantilevered transverse arch of a mammal, lateral
view; E, forces acting on mammalian pelvis in erect posture, lateral view.
109
110
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
ulum and sacroiliac articulation and this is by
far the most destructive force to which this part
of the arch is subjected.
The rotational force acting on the sacroacetab-
ular axis produces a powerful rotational shear or
torque on the sacroiliac articulation, similar to
that on a bolt being tightened by a wrench. This
force would tend to displace the anterior part of
the articulation downward, the posterior part up-
ward. The posterior upward force of the couple is
counteracted by the firm union of the auricular
surfaces of the sacrum and ilium. The anterior
downward force is met by the shape of the sacrum,
which is wedged between the ilia like an inverted
keystone (fig. 60, B, a). This angle is about 15
in Canis, and rises to 40 or more in the Bovidae.
In the bears and Ailuropoda, in which the articu-
lation is synostotic, the angle approaches zero, and
this is also true in the giant anteater {Myrmeco-
phaga), where the joint is fused.
During locomotion the sacro-iliac articulation is
also subjected to momentary horizontal thrust
(fig. 60, D, H) that tends to displace the ilium
anteriorly on the sacrum. This force results from
the anterior thrust of the hind legs, and is espe-
cially evident during galloping or leaping, when
the femur is nearly or quite in line with the sacro-
acetabular axis, as is evident in Muybridge's (1957)
photographs of horses and dogs. This force is
counteracted by the wedge shape of the sacrum in
the frontal plane : the bone is wider anteriorly than
posteriorly. The plane of the auricular surface
forms an angle with the mid-sagittal plane of
11-14 in Canis, Ursus, and Ailuropoda, and in a
specimen of Bison this angle amounts to 34.
Forces on the Pelvis in the Erect Posture
If a quadruped stands erect on its hind legs the
forces acting on the pelvis are approximately dou-
bled, since the pelvis then bears the entire weight
of the animal. They are also significantly altered
in direction. The transverse arch still functions
as before, but the ilia are no longer cantilevered to
the sacrum. The thrust is now along the sacro-
acetabular axis (fig. 60, E, T). Instead of shear-
ing forces along the sacroacetabular axis there is
now compression. The rotational shear at the sa-
croiliac articulation is converted into a simple
shear, which is largely or entirely counteracted by
the wedge shape of the sacrum. This is a stronger
construction than in the quadrupedal posture, but
most of the elasticity is gone; if the sacroiliac ar-
ticulation fuses there is virtually no elasticity in
the pelvis.
Horizontal forces, i.e., forces approximately par-
allel to the sacro-acetabular axis, predominate in
burrowing animals that use their hind legs for brac-
ing while digging. Thus the dominant forces act-
ing on the pelvis in such forms are very similar to
those in the erect posture, and this is reflected in a I
striking similarity in pelvic architecture.
Examination shows that seven features charac-
terize the pelvis in mammals in which forces par-
allel to the long axis of the pelvis predominate,
i.e., those that stand erect and those that use their
hind legs for bracing while digging. These are:
1. The wings of the ilia tend to shift into the frontal
plane.
2. The pelvis is short anteroposteriorly.
3. The sacroiliac articulation is strengthened by includ-
ing additional sacral vertebrae (increased area) and/or
by strengthening the joint through interlocking bony
processes, synostoses, etc.
4. The lateral diameter of the corpus of the ilium is
increased, and it tends to become circular in cross
section.
5. The pubo-ischiadic symphysis is greatly shortened.
This reduction is in the anterior part of the symphysis.
6. The total number of sacral vertebrae is increased.
7. The tail is usually, but not always, shortened.
In marsupials Elftman (1929) attributed the
shape of the wing of the ilium anterior to the sacro-
iliac joint chiefly to the "sizes of the three muscle
masses whose areas of origin form its three borders
the erector spinae mesially, the gluteus medius
and gluteus minimus dorso-laterally, and the ili-
acus ventro-laterally." Waterman (1929) con-
cluded that the form of the ilium in primates is
largely determined by muscles. Elftman believed
that in Vombatus, however, the width of the trunk
is partly responsible for the lateral flare of the an-
terior part of the ilium.
In the bears and Ailuropoda the mass of the
middle and deep gluteals is relatively no greater
than in the cursorial dogs and cats (see Table 15).
Even in man the relative mass of these muscles is
no greater than in cursorial carnivores. The ilio-
psoas in Ailuropoda is slightly heavier than in
bears and dogs but it is smaller than in the lion,
which has a notably narrow pelvis. In the lion
the great size of the iliopsoas (almost identical
with man) is associated with leaping.
If the relative masses of the large muscles at-
taching to the wing of the ilium are nearly con-
stant, then differences in size, shape, and slope of
the iliac wing must be attributable to other causes.'
The most consistent character of the iliac wing in
' The long iliac crest (= broad iliac wing) characteristic
of bears must be attributable to pecularities, still unknown,
in the abdominal wall muscles and iliocostalis that attach
to this crest. Elsewhere among carnivores the crest tends
to be short in climbing and aquatic forms, "normal" in ter-
restrial forms.
Iliac Crest Descending Rannus Ischium
Cams lupus
Gulo luscus
Procyon lotor
Ursus orctos
Ailuropoda
melanoleuca
Fig. 61. Anterior views of pelves of carnivores, to show angle of inclination of iliac and ischiadic planes.
Ill
112
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
mammals in which forces parallel to the long axis
of the pelvis predominate is that the wing tends
to shift into the frontal plane (fig. 61). The iliac
crest forms an angle with the frontal plane of 20
21 in Ailuropoda, 22 in a Mellivora, 28 in a
Meles, and only 12 in a Vombatus. In the bears
and American badgers the slope of the crest is
about normal for terrestrial carnivores, 45-50. In
the cursorial wolf the slope approaches the verti-
cal, 70-80 (fig. 61).
The main advantage of a frontal position of the
wing of the ilium is leverage; in both the erect and
the burrowing posture the gluteals and iliacus are
in an increasingly favorable position to stabilize
the pelvis and vertebral column as these muscles
approach the frontal plane. Waterman (1929) has
discussed the relation between erect posture and
the muscles attaching to the iliac crest in primates.
The muscles attaching to this crest in Ailuropoda
are shown in figs. 56-58; the corresponding rela-
tions in other carnivores are unknown.
Shortening of the pelvis is symmetrical, affect-
ing the preacetabular and postacetabular regions
about equally. The pelvis is almost as short in
bears (index 36) as in the panda, and is only slightly
longer in Meles (41) and Taxidea (41). Mellivora
is a striking exception (index 50). The norm for
terrestrial carnivores is about 46. The advantage
of reduction in pelvis length with increased hori-
zontal forces on the pelvis is not clear to me.
Strengthening of the sacroiliac articulation with
increase in horizontal forces on the pelvis is so ob-
viously functional that it requires no comment.
It reaches a maximum in the Myrmecophagidae,
in which the sacroiliac articulation is supplemented
by a strong sacroischiadic articulation occupying
the normal site of the sacrotuberous ligament. In-
creased diameter of the body of the ilium is like-
wise associated directly with increased horizontal
thrust; relative diameter of the body reaches a
maximum in the Old World badgers.
Shortening of the symphysis is invariably corre-
lated with increased horizontal thrust on the pel-
vis. It is seen in the wombat (Marsupialia), the
extinct ground sloths and the anteaters (Edentata),
the anthropoids (Primates), and in badgers and
Ailuropoda among the carnivores. The symphysis
is also short in aquatic forms: in the otters and
particularly so in the seals.
Various attempts, all more or less speculative,
have been made to explain reduction in length of
symphysis. All explicitly or implicitly regard sym-
physis length as proportional to the forces the
symphysis must withstand. Weidenreich (1913)
attributed shortening of the symphysis in primates
to the weight of the viscera and the pull of the
sacrotuberous and sacrospinous ligaments drawing
the pubic rami apart. Mijsberg (1920) suggested
that vertical forces acting on the pelvis in quad-
rupeds produce exorotation of the coxa around the
sacrum, and that this exorotation is resisted by
the symphysis, whose length is proportional to the
exorotatory force. Mijsberg's interpretation is
supported by the fact that the seals (Phocidae),
in which vertical forces acting on the pelvis are
negligible or absent, have no true symphysis.
Elftman (1929) accepted Mijsberg's explanation,
but suggested further that in Vombatus shorten-
ing of the symphysis posteriorly is necessary to
provide a proper outlet for the pelvis. Nauck
(1938) believed he could detect a correlation be-
tween dorsal shifting of the acetabulum which
he maintains would reduce the exorotatory forces
on the pelvis and reduction in symphysis length.
Nauck's correlation exists only in selected cases,
and obviously is not a general explanation.
All investigators' agree that the iliopubic arch
functions primarily as a tie to counteract horizon-
tal thrust ("exorotatory forces") developed in the
dorsal iliosacral arch. All agree further that re-
duced symphysis length is somehow associated
with reduced tensile stresses in the iliopubic arch.
The resolution of vertical vs. horizontal forces
within the pelvis has not been demonstrated ex-
perimentally, however, and consequently all expla-
nations are conjectural. A correlation between
increased force parallel to the long axis of the pel-
vis and reduced symphysis length remains as an
empirical fact.
Increased sacral length behind the sacroiliac ar-
ticulation is associated with increased horizontal
thrust on the pelvis both in forms that stand erect
and in those that use their hind legs for bracing
while digging. Extending the sacrum posteriorly
increases the attachment area for the multifidus
and sacrospinalis muscles. The main action of
both of these muscles is to extend the vertebral
column when acting on the vertebrae, or to extend
the pelvis when acting on the sacrum. These ac-
tions are obviously important for spinal fixation
both in the erect posture and in burrowing.
It seems likely that reduction in tail length is
a consequence of increased sacral length, although
critical data are lacking. If sacral length is in-
creased to provide additional area for the spinal
erectors, this area could be provided only at the
expense of the basal tail muscles. The special
cases of long sacrum associated with long tail in
the anteaters and aardvark suggest a fundamental
difference in either the spinal erectors or the caudal
' Braus (1929, p. 456) interprets the human pelvis as a
ring under spring-like internal tension.
DAVIS: THE GIANT PANDA
113
muscles in these forms, but pertinent data are
lacking.
The Pelvis of Ailuropoda. The pelvis of the
giant panda is notably different from that of the
bears, which it resembles no more closely than it
does the pelvis of several other arctoid carnivores.
The bear pelvis, in turn, is unique among arctoids
in its combination of long iliac crest, very broad
iliac wing with normal slope in the transverse
plane, and extremely long symphysis.
The pelvis of Ailuropoda exhibits, to a far gi-eater
degree than any other carnivore, the seven features
that characterize the mammalian pelvis when forces
parallel to the body axis predominate (p. 110).
These forces predominate during burrowing, and
when the animal stands erect on its hind legs.
Ailuropoda is not a burrower, nor does it stand
erect to any greater extent than do the bears.
There is, in fact, no reason for believing that hori-
zontal forces on the pelvis in Ailuropoda are gr-eater
or more sustained than in Ursus or other carni-
vores. This indicates that some other (non-adap-
tive) factor is responsible for the form of the pelvis
in Ailuropoda.
The pelvis adjoins the lumbosacral region of the
body axis. In this region in Ailuropoda the axial
skeleton, the urogenital system, and the circula-
tory system all show non-adaptive deviations from
the norm. The most plausible explanation for the
pelvic form in Ailuropoda is that it reflects the
serious disturbance in the axial gradiant that is
associated with cephalization (p. 84).
2. Femur
The femur in the Carnivora serves for the origin
or insertion of 22 muscles. Of these, 15 belong to
the hip joint and 7 to the knee joint or lower leg
and foot. In the Carnivora the form and archi-
tecture of the femur are determined largely by the
static requirements of support, to a far greater
degree than for the humerus. Except for the tro-
chanters, the external form of the femur is scarcely
modified by the muscles that attach to it.
It was found (Table 2) that if femur length is
calculated against the length of three thoracic ver-
tebrae, the femur in Ailuropoda is longer than the
norm for carnivores but not so long as in Ursus.
Relative femur length of the panda is similar to
that of the cats, whereas the bear femur is among
the longest known for the Carnivora, equal to
Crocuta and exceeded only by Chrysocyon.
If the position of the acetabulum remains rela-
tively constant (as it does among arctoid carni-
vores; see Table 11), then a long femur would re-
sult in fast but weak movements of the femur
around the acetabulum, as compared with a short
femur.' From the standpoint of locomotor effi-
ciency, the ratio between femur length and tibia
length is much more significant than is femur length
relative to pelvis length.
The femur of Ailuropoda (fig. 62) is similar in
form to that of Ursus and the Procyonidae, with
a low greater trochanter and a straight shaft. As
in most arctoid carnivores, the bone shows little
torsion.^ In two wild-killed pandas the torsion
angle is 1 and 3; in a third, reared in cap-
tivity, it is 13. The mean of twelve wild-killed
arctoids is about 1, extremes 3 to +14. Four
wild-killed Ursus range from 2 to -t-14, mean
+2. The greatest torsion among arctoids is in
the Procyonidae: 10 and 14 in two individuals of
Procyon, 6 in a Nasua. Torsion in two cage-
reared Ailurus is 3 and 12.
In Ailuropoda the head of the femur is hemi-
spherical, about 38 mm. in diameter, slightly
larger than in a bear of comparable size. The
fovea, for the ligamentum teres, occupies the same
position as in Ursv^, but is wider and deeper.
The neck is distinct, and forms an angle of about
130 with the shaft; it is slightly more angulated
than in Z7rsMS (134-138) or Proc|/ow (135). Angu-
lation of the neck is 125-140 in arctoid carnivores
in general. The neck is narrower anteroposteri-
orly but slightly wider dorsoventrally than it is in
Ursus.
The greater trochanter, which provides at-
tachment for the middle and deep gluteals and
the piriformis, does not differ significantly from
that of Ursus. It is a broad knoblike structure
scarcely rising above the level of the neck. Its
anterior border is continued distally as a low crest
that terminates at the level of the lesser trochanter
in a prominent scar, the gluteal tuberosity, mark-
ing the insertion of the superficial gluteal muscle.
The trochanteric fossa, which receives the ten-
dons of the obturator muscles, is deep and well
defined. The lesser trochanter, on which the
iliacus and psoas major muscles attach, is a low
conical eminence projecting posteromedially, as in
other arctoid carnivores. A crescent-shaped trans-
verse scar extending across the posterior surface
of the bone, from the lesser trochanter nearly to
the gluteal tuberosity, marks the attachment of the
quadratus femoris.
' Disregarding differences in tension and velocity of con-
traction of muscles. See Maynard Smith and Savage (1 956)
for methods of calculating relative mechanical advantages
in limbs.
* Torsion was measured by the method given by Schmid
(1873). My figures do not always agree with his, and I sus-
pect this is because many of his skeletons were from zoo
animals.
114
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Lig. teres Jeiiioris
Fossa Irochaiile
Capauta arlictilaris ^***"^\ "
TiiH-haiiler minor.
M. iliacus & psoas major
M. quadratus femoris
M. vastus nied.
M. adductor
Capsitla articuhiris
M. gastroc. (cap- nied.'i
Lig. criic.
M. pjTiformis
Trochanter major
M. glutaeus medius .
M. obturator int.
M. glutaeus prof. ,
M. obturator ext.
M. glutaeus superf.
M. pjTiformis
Tuber, glulaea
M. vastus lateralis
M. adductor pars post
M. adductor pars ant
Epicomlijliis lateralis
M. plant. & gastroc,
(cap. lat.)
Capsula arlicularis
Colltim femoris
M. iliacus & psoas major
M. vastus intermedius
Lig. coll. fihujare
Plica synorialii patellaris Lig. cnic. ;)<)S( \M. poplitcus
M. gastroc.(cap. med.)
Lig, coll. libiale
Capsula articttlaris
M. e.\t. dig. longus
Fig. 62. Right femur of Ailuropoda, posterior and anterior view.
The shaft of the femur is nearly or quite straight ;
it is convex anteriorly to a greater or lesser degree
in Ursus and other arctoids. The anterior surface
is faintly reticulated. As in other arctoids the shaft
is wider transversely than anteroposteriorly: the
ratio is about 80. The linea aspera on the poste-
rior surface of the shaft is scarcely indicated, even
less so than in Ursus. Slight roughenings on the
proximal two thirds of the shaft mark the attach-
ments of the pectineus and adductor muscles;
these are wanting in the distal third of the bone
where the femoral vessels are in contact with the
bone. The anterior, medial, and lateral surfaces
of the shaft are overlain by the vastus muscles,
and are devoid of any modeling.
The inferior end of the femur differs in details
from that of Ursus. The condyles are roller-like,
rather than ball-like as in Ursus and other arc-
toids, and the intercondyloid fossa (in which the
cruciate ligaments attach) is relatively broader.
The lateral condyle is wider and longer than its
fellow and its articular surface is more oblique.
DAVIS: THE GIANT PANDA
115
The lateral epicondyle contains a large crater-like
depression in which the lateral collateral ligament
attaches; the plantaris and the lateral head of the
gastrocnemius arise from the prominent superior
rim of the crater. A dimple-like depression imme-
diately below the crater marks the attachment of
the popliteus. The median condyle is much
narrower than the corresponding condyle in Ur-
sus, as a result of encroachment by the intercon-
dylar fossa. The medial epicondyle contains a
large depression for the medial collateral ligament;
its anterodorsal rim is elevated into a prominent
tubercle on which the medial head of the gastro-
cnemius arises. The patellar surface does not dif-
fer from the corresponding area in Ursus and
other arctoids.
The femur of Ailuropoda thus differs from that
of Ursus chiefly in details of modeling, torsion,
and angulation features that certainly represent
post-natal adaptive adjustments. The only fea-
ture that cannot be so interpreted is the relative
length of the femur in Ailuropoda, which probably
demands a genetic basis. I can find no mechan-
ical explanation for the shortening of this bone in
Ailuropoda relative to Ursus; the matter is dis-
cussed further on p. 38.
3. Patella
The patella (fig. 63) is ovate, about 37 mm. long
by 32 mm. wide. It is relatively wider and more
disk-shaped than the corresponding bone in Ursus,
but is otherwise very similar. The anterior sur-
face bears longitudinal striae. The ai-ticular surface
is broader than high, and the lateral and medial
articular facets are not clearly marked. The scar
for the attachment of the quadratus femoris ten-
don is prominent on the superior and lateral sur-
faces, as is the attachment area for the patellar
ligament on the anterior surface at the apex.
4. Tibia and Fibula
The tibia and fibula are very short. These bones
are also short relative to other limb segments in
Ursus, and are very short in badgers (Table 2).
Short distal segments result in relatively powerful
but slow movements in the distal part of the limb.
Hence the advantage of a low femorotibial index
in graviportal animals and in digging forms that
use the hind legs for bracing.
The tibia (fig. 63) is basically similar to that of
Ursus. It differs chiefly in being shorter and more
compact, and in the greater torsion of the distal
end. The head, which measures 65-70 mm. in
transverse diameter, is relatively broader than in
Ursus. The lateral condyle is about the same
size as the medial, as in the bears. A crater-like
depression on its lateral side, for the attachment
of the lateral collateral ligament, is larger but shal-
lower than in Ursus. The lateral articular surface
is ovate, its anteroposterior diameter greatest; it
encroaches on the anterior intercondyloid fossa
more than in Ursus. The medial condyle pro-
jects medially some distance beyond the border
of the shaft. The articular facet for the head of
the fibula lies farther posterior than in Ursus, but
is otherwise similar. The medial articular surface
is almost circular in outline. Both the anterior
and the posterior condyloid fossae are wider than
in the bear. The tibial tuberosity, on which the
patellar ligament attaches, is prominent in Ursus
but is scarcely indicated in Ailuropoda.
The shaft of the tibia is almost straight. It is
bowed very slightly medially, as in Ursus, and
this bowing appears to be (but is not) exaggerated
by the medial extension of the proximal and distal
ends of the bone. This latter circumstance greatly
increases the interosseous space between tibia and
fibula, and the total width across the leg (from
medial border of tibia to lateral border of fibula).
The shaft is most slender near the middle, flaring
somewhat both proximally and distally. The an-
terior crest, which is associated with the insertions
of the gracilis, sartorius, biceps, and semitendino-
sus, is well marked, especially proximally; it con-
tinues distally into the medial malleolus. The
interosseous crest on the lateral surface of the
shaft, on which the interosseous membrane at-
taches, is a prominent ridge beginning below the
lateral condyle and extending down to the distal
fibular articulation. On the posterior surface of
the shaft several ridges mark the boundaries be-
tween the flexor hallucis longus, the tibialis poste-
rior, and the popliteus (fig. 63).
The distal end of the tibia is very similar to that
of Ursus, except that it is rotated farther on the
shaft; the torsion angle of the transverse axis of
the distal end against the bicondylar axis of the
proximal end is 35-48 in Ailuropoda, whereas in
Ursus it is only about 20. The transverse axis
also is inclined more obliquely with respect to the
long axis of the bone: about 120 in Ailuropoda,
about 105 in Ursus. The medial malleolus is
short and wide anteroposteriorly. A deep groove,
the sulcus malleolaris, on its posterolateral surface
lodges the tendon of the posterior tibial muscle; a
similar groove is present in Ursus. The inferior
articular surface, which articulates with the as-
tragalus, is ovate, wider medially and narrower
laterally than in Ursus. It bears a median ridge,
bounded on either side by a depression, that fits
a corresponding surface on the astragalus. At the
lateral end of the articular surface is a small
116
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
M. vastus lato^is
M. rectus femoris
Lig. paleUae
M. tibialis a(it
Condylus lot
M. peronaeus longus
M. soleus
Lig. eoll. fibulare
M. flex, hallucis longus
M. peronaeus tertius
M. tibialis ant.
M. vastus med.
M. sartorius
Lig. patellae
M. semimembranosus
Condylus med.
M. peronaeus brevis
M. ext. hallucis longus
M. peronaeus longus
CapstUa artieularis
M. popliteus
M. flex, hallucis longus
M. tibialis post.
M. gracilis
Sulcus malleolaris
Malleolus med
Capsula artieularis
M. tibialis post.
M. flex. dig. longus
M. soleus
M. tibialis post.
M. flex, hallucis
longus
M. peronaeus bre\TS
Capsula artieularis
Malleolus lot.
M. tibialis post.-/^
M. peronaeus brevis'
vM. peronaeus tertius
Fig. 63. Right patella, tibia, and fibula of Ailuropoda; anterior and posterior views.
obliquely situated articular facet for the distal
end of the fibula.
The fibula (fig. 63) is slightly heavier than the
fibula of Ursus, and is bowed slightly laterally,
which further exaggerates the transverse diameter
of the leg. It articulates with the tibia by a syno-
vial joint at each end and therefore, as in Ursus,
represents the mobile type of fibula.
The head is an expansion of the proximal end
differing from that of Ursus only in minor details.
The articular facet is a flat ovate surface, set
obliquely and directed medially and posteriorly.
No scar marks the attachment of the lateral col-
lateral ligament on the lateral surface immediately
below the head. The shaft is triangular in cross
section throughout most of its length, but is con-
siderably flattened distally. Almost its entire sur-
face provides attachment for muscles, of which
seven arise from the shaft, and roughened longi-
tudinal elevations on the shaft mark the attach-
ments of aponeuroses and intermuscular septa
separating many of these muscles. The most con-
spicuous crest, on the medial surface, is the inter-
osseous crest to which the interosseous membrane
attaches.
The distal end of the fibula is an irregular ex-
pansion, larger than the proximal expansion, that
forms the lateral malleolus. It is relatively larger
and heavier than the lateral malleolus of Ursus,
but is otherwise comparable. The lateral malle-
M. tibialis ant-
Os cuneiforme 1
Os cuneiforme 2.
Os naviculare
Os sesamoid, tib.
M. flex. dig. quinti brevis
peronaeus brevis
Os cuneiforme 3
M. abductor dig. quinti
Os cuboideum
M. tibialis post
Capsula articularis
Calcaneus
Fig. 64. Right tarsus and metatarsus of Ailuropoda, dorsal view.
M. flex. dig. quinti brevis
M. abductor dig. quinti
M. peronaeus longus
M. quadratus plant.
Tendo m. plantaris
M. soleus & gastrocnemius
M. peronaeus longus
M. tibialis ant.
M. flex, hallucis irevis
M. abductor dig. quinti
Tendo m. plantaris
Fig. 65. Right tarsus and metatarsus of Ailuropoda, plantar view.
117
118
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
olus does not project so far distad as the medial
malleolus, and its articular surface is less extensive
anteroposteriorly. The lateral surface bears a
prominent elevation, the processus lateralis fibu-
lae (new name), that separates the peroneal ten-
dons into two groups; the long peroneal tendon
lies immediately anterior to the process, while the
tendons of the brevis and tertius lie immediately
behind it. In Ursus this process is a sharply pro-
jecting knob-like structure, and in other carnivores
(except the Canidae) it forms a hook that arches
backward over the tendons of the peronaeus brevis
and tertius. The medial surface of the malleolus
bears two articular surfaces: a smaller proximal
one facing proximally and medially that articu-
lates with the tibia, and a larger distal one facing
distally and medially that articulates with the
astragalus.
5. Tarsus
The tarsus (figs. 64, 65) is in general more con-
servative than the carpus. The tarsus of living
procyonids actually differs little from that of the
more generalized Paleocene creodonts, in which it
is adapted to arboreal life ( Matthew, 1937, p. 317) ;
and the tarsus of modem bears is strikingly sim-
ilar to that of the Middle Paleocene creodont
Claenodon. In the bears the ankle shows a char-
acteristic shortening and broadening of all the
tareal bones; this is also evident, though less pro-
nounced, in Ailuropoda.
The tarsus of Ailuropoda is, in fact, moi-phologi-
cally more "primitive" than that of Ursus. This
is seen in the less pronounced broadening of all the
tarsal bones, in the presence of a large astragalar
foramen, and particularly in the form of the two
transverse ankle joints the transverse tarsal and
tarsometatai^sal joints (fig. 65). In Ltsws both of
these joints are essentially continuous across the
ankle (as in man), whereas in Ailuropoda and gen-
eralized carnivores both joints consist of two or
more transverse segments offset from each other.
The ursid-human form of these joints is a second-
ary adaptation to plantigrade walking, whereas
the interrupted joints seen in more generalized car-
nivores increase the lateral stability of the tarsus.
A unique feature of the tarsus of Ailuropoda is
the extraordinarily loose fit between the astragalus
and calcaneus. The lateral and medial articular
surfaces of the two bones cannot be brought into
congi'uence at the same time, but only alterna-
tively by sliding the astragalus sideways over the
calcaneus. In association with this, the diameter
across the two articular surfaces on the astragalus
gieatly exceeds the diameter across the correspond-
ing surfaces on the calcaneus.
The astragalus (BXA: talus) (fig. 66) is rela-
tively larger than in Ursus, but differs chiefly in
its longer neck and narrower head, and in the
presence of a large astragalar foramen. The troch-
lea is broader than long, and is characterized by a
very shallow gi-oove and relatively small malleolar
surfaces; the upper tarsal joint is less secure and
permits greater lateral rotation than in Ursus.
The superior articular surface is not continued
posteriorly over the posterior process as in pro-
cyonids. The arc of the trochlea is thereby re-
duced by about 35; it measures about 165 in
Ailuropoda and Ursus, and about 200 in procy-
onids.
The medial malleolar surface, which in Ursus
extends over the neck nearly to the margin of the
head, reaching as far distad as does the lateral
malleolar surface, is much shorter in Ailuropoda,
ending at the base of the neck. The lateral mal-
leolar surface is similar to that of Ursus except
that it is flatter. Immediately posterior to the
trochlear gi-oove there is a large astragalar fora-
men in all specimens examined. This foramen,
characteristic of creodonts, occurs sporadically
among generalized modem procyonids iBassaris-
cus) and mustelids {Gulo, Taxidea); I also find a
small astragalar foramen in one specimen of Ursus
americanus. Behind the trochlea a deep groove
for the flexor hallucis longus tendon is present in
Ursus and other carnivores; this groove is want-
ing in Ailuropoda.
On the inferior surface the lateral (posterior in
human anatomy) and medial articular surfaces,
articulating with con-esponding articular surfaces
on the calcaneus, resemble those of Ursus. They
are oblong, relatively shallowly concave areas sep-
arated by a deep astragalar gi-oove. The lateral
is more extensive than the medial, and in Ailu-
ropoda their axes diverge slightly distally. As in
other camivores, the medial articular surface lies
mostly beneath the neck of the astragalus. Of the
accessory facets (Davis, 1958) only the anterior
marginal facet of the medial articular surface is
represented. It is a narrow extension of the medial
surface, continuous anteriorly with the na\-icular
articular surface, and it rests on the cuboid.
The head and neck, on the contrary, resemble
those of procyonids and generalized mustelids and
viverrids more closely than they do those of Ur-
sus. The neck is relatively long, nan-ower than in
Ursus, and deflected toward the medial border of
the foot, foiTning an angle of about 98 with the
transverse axis of the trochlea. The head bears
two articular surfaces, as in other camivores: an
oval convex area anteriorly and medially for the
navicular, and a small triangular area inferiorlj'
DAVIS: THE GIANT PANDA
119
Ailuropoda
Ursus
Fig. 66. Opposing surfaces of right astragalus and calcaneus of Ailuropoda and Ursus arctos.
and laterally for the cuboid. On the inferior sur-
face, immediately behind the navicular articular
surface, a deep pit marks the attachment of the
talocalcaneal interosseous ligament.
The calcaneus (fig. 66) is longer and more slen-
der than in Ursus. On the superior surface the
lateral articular surface is an elongate oval, ex-
tending farther posteriorly than in Ursus. As in
bears, it describes a continuous spiral track: an-
teriorly it faces slightly laterally, while its poste-
rior end is almost vertical, facing medially. This
articular surface is scarcely curved in cross section,
and the curvature along the long axis is relatively
slight; in this flatness the bears and panda differ
sharply from other carnivores. The medial artic-
ular surface is a flat discoidal area on the superior
surface of the sustentaculum. As in Ursus, the
posterior end of this articular surface is deflected
sharply downward, forming an angle of almost 90
with the main articular surface. This arrange-
ment, which is present in Nasua and indicated in
Gulo but is wanting in other carnivores, increases
stability of the lower tarsal joint at the expense of
mobility.
The medial articular surface is continued ante-
riorly into a narrow accessory facet that extends
forward to the anterior border of the calcaneus,
articulating with the anterior marginal facet of the
astragalus. This accessory facet, which increases
the stability of the lower tarsal joint, is present in
most, but not all, carnivores.
120
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Opposite the sustentaculum the lateral surface of
the calcaneus is produced into a prominent projec-
tion, the coracoid process (Baum and Zietzschmann,
1936), from which arise the extensor digitorum
brevis and quadratus plantae muscles. In Ursus
the coracoid process is a long shelf-like structure
extending posteriorly to the posterior border of
the lateral articular surface, while in other carni-
vores it is less extensive.
The cuboid articular surface is more oblique than
the coiTesponding surface in Ursus but is other-
wise similar. The posterior end of the calcaneus
is expanded into a knob-like structure. Almost
the entire posterior face is occupied by a large de-
pressed scar that marks the attachment of the
tendo Achillis and its associated bursa.
The navicular articulates with the astragalus,
the cuboid, and the three cuneiforms, as in Ursus
and other carnivores. The posterior surface is
composed almost entirely of a large ovate concave
articular facet that receives the head of the astrag-
alus (fig. 64). The anterior surface is convex, its
superior part indistinctly divided into three facets
for the three cuneiform bones; inferiorly it is
roughened at the attachment site of the plantar
naviculari-cuneiform ligaments. On the medial
surface a smooth prominence marks the articula-
tion site of the tibial sesamoid. A narrow articu-
lar facet on the inferolateral surface articulates
with the cuboid, and immediately mesad of this
on the inferior surface is a rounded prominence,
the navicular tuberosity.
The cuboid resembles that of Ursus in shape,
but is relatively longer and narrower.' Its poste-
rior surface presents a rectangular convex articular
surface for the calcaneus (fig. 64) ; its anterior sur-
face bears a slightly concave surface for the fourth
and fifth metatarsals, a faint ridge dividing the
two areas. Its medial surface presents two artic-
ular surfaces, a vertical surface posteriorly that
articulates with the head of the astragalus, and an
irregularly shaped surface that articulates with the
navicular and the third cuneiform. The inferior
surface bears a prominent transverse ridge for the
attachment of the long plantar ligament.
The cuneiform bones articulate with the na-
vicular posteriorly and the first three metatarsals
anteriorly. The first is the largest ; the tibial sesa-
moid articulates partly with its posteromedial cor-
' The tarsus and pes are relatively broader in bears than
in other carnivores. It is interesting and suggestive that the
relative breadth of the cuboid increases with absolute size
in the genus Ursus. The ratio breadth 'length X 100 in a
series of bears is: Ursus americanus 81, U. arctos 92, U. gyas
95. The only available specimen of U. spelaeus is a shade
smaller than my very large U. gyas and has a ratio of 94.
The corresponding ratio for Ailuropoda is 64.
ner. The third cuneiform articulates laterally with
the cuboid.
The tibial sesamoid is relatively much larger
than in Ursu^ (fig. 54); it measures 20 mm. in
length by 13 in breadth. As in other carnivores,
it articulates with the navicular and first cunei-
form. The bone is flattened from side to side.
The tendon of the posterior tibial muscle inserts
on its posterior border, and a part of the flexor
hallucis brevis muscle arises from its medial face
(fig. 102).
6. Pes
The metatarsals decrease in length from the
fifth to the first; in Ursus the fourth is the longest,
and in procyonids the third and fourth are sub-
equal. As in Ursus, the metatarsals are short.
The fifth is relatively heavier than in Ursus, but
the others are of comparable size. As in other
carnivores, the proximal end of the fifth metatar-
sal bears a prominent lateral process to which the
tendon of the peroneus longus and brevis and the
abductor digiti quinti attach. j
As in the manus, the distal articular surfaces of '
the metatarsals are narrower than in Ursus, and
the median ridge is more prominent.
The phalanges are similar to those of Ursus,
relativelj- shorter than those of the procyonids.
In the proximal row a pair of elevations on the
inferior surface of each bone, near the distal end,
marks the attachment of the interosseous muscles.
A conspicuous pit-like excavation on the inferior
surface of each bone of the middle row, immedi-
ately behind the trochlea, receives the large plantar
process of the terminal phalanx.
A pair of sesamoid bones is present beneath
the metatarsophalangeal articulation of each digit.
There are ten in all.
B. Review of the Hind Leg
The bones of the hind leg of Ailuropoda, like
those of the fore leg, agree with the corresponding
bones of Ursus in all essential respects. As in the
fore leg, differences in details of modeling, torsion,
and angulation probably represent postnatal re-
sponses to stresses extrinsic to the bone tissue itself.
Relative lengths of limb segments agree with the
proportions in graviportal animals. This suggests
that limb proportions in Ailuropoda are broadly
adaptive, although the animal is much too small
to be truly graviportal and the adaptive signifi-
cance, if any. of the limb proportions is not clear.
Short distal segments result in relatively powerful
but slow movements in the distal part of the limb.
Hence the advantage of a low femorotibial index
to heavy graviportal animals and to digging forms
that use the hind limbs for bracing. Length of
Cloenodon cofruqatus
Potos flavus
Ursus arctos
Ailuropodo melonoleuca
Fig. 67. Right tarsus and pes of representative carnivores. The small inset to the left of Claenodon corrugatus is Claenodon
montanensis (Bull. U.S. Nat. Mus., 169).
121
122
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
long bones is certainly gene-controlled, but the
mechanism of such control is unknown.
Fuld (1901) demonstrated a slight but signifi-
cant increase in tibia length in dogs that had been
bipedal since puppyhood. Colton (1929) found
that in the rat, on the contrary, bipedalism results
in a slight increase in femur length. In neither
the dogs nor the rats was the difference anywhere
near as great as the difference between the relative
lengths of these bones in Ailuropoda and Ursus.
The hypertrophied tibial sesamoid is a product
of natural selection, but of selection acting on the
radial sesamoid. The fact that the tibial sesamoid
has hypertrophied along with the radial sesamoid
shows that these two bones are homeotic from the
genetic standpoint as well as serially homologous
from the morphological standpoint.
Thus only one (presumably) adaptive feature in
the bones of the hind leg the relative lengths of
the long bones appears to result directly from
natural selection acting on the bones themselves.
Even this does not appear to be adaptive and may
be a pleiotropic effect.
VII. DISCUSSION OF OSTEOLOGICAL
CHARACTERS
It is evident from the foregoing description that
the skeleton supplies abundant and convincing
evidence that Ailuropoda is much closer to the
Ursidae than to any other group of living carni-
vores. Missing "ursid characters" have been partly
responsible for disagreement among mammalogists
as to the affinities of Ailuropoda (e.g., Mivart,
1885a; Weber, 1928). It is now obvious that these
missing characters have been obliterated by phylo-
genetically recent factors that for the most part
are extrinsic to the skeleton. The most important
of these extrinsic factors is hypertrophy of the
skeletal musculature. Yet, despite close similarity
in all essential respects, the panda skeleton differs
from the bear skeleton in a number of very puz-
zling ways. It is the interpretation of these differ-
ences that is pertinent to our central problem.
The panda skeleton resembles the bear skeleton in
all essential respects.
The bear skeleton itself differs from the general-
ized carnivore condition in a number of features
that cannot be interpreted as adaptive, and I am
certain that many ursid characters represent what
Griineberg (1948) has called "subordinated gene
effects" effects that are genetically, physiologi-
cally, or even mechanically connected with a pri-
mary gene effect on which natural selection has
operated, without themselves being adaptive. Such
non-adaptive characters might persist indefinitely
if selection against them is less intense than selec-
tion for the primary effect. Among the most con-
spicuous of these in the bears are limb proportions,
curve of moments of resistance in the vertebral
column, shortness of lumbar region, shortness of
tail, length of sacrum, form of pelvis. Ailuro-
poda shares most of these characters with Ursus,
and has superimposed additional features, likewise
mostly non -adaptive, on the ursid pattern.
Many of the differences between panda and bear
skeletons are adaptive, but their cause is extrinsic
to the bone itself; that is, they merely reflect the
response of the bone tissue to external pressures,
stresses and strains, and other purely mechanical
factors. In the absence of the appropriate stimu-
lus such characters fail to appear. Among such
features are the surface modeling of bones, tor-
sions, form and extent of articular areas, and size
and position of foramina. These are characteristic
features of the skeleton of Ailuropoda, and they
may be clearly adaptive in the sense of promoting
the efficiency of the organism, but they are epi-
genetic to the bone and therefore are not the result
of natural selection on the skeleton.
The most conspicuous way in which the skeleton
of Ailuropoda differs from that of Ursus is in a
general increase in the quantity of compact bone
throughout the entire skeleton. Except for mas-
ticatory requirements, no differences from the
habits of bears would demand such increased thick-
ness of compacta for mechanical reasons. A gen-
eralized effect of this kind, involving an entire
tissue and with sharply localized advantage to the
organism, would almost surely have a single cause.
Comparable generalized effects, involving the whole
skeleton and localized in a single genetic factor,
are well known in laboratory and domestic ani-
mals (Stockard, 1941; Griineberg, 1952; Klatt and
Oboussier, 1951). Wherever they have been ana-
lyzed, it has been found that such effects are me-
diated through the endocrine system. We may
postulate that in the panda, because of mastica-
tory requirements, selection strongly favored in-
creased thickness of compacta in the skull. This
increase was actually achieved via a process that
results in generalized thickening of the compacta
throughout the skeleton. The functionally un-
necessary increase of bone tissue in the postcranial
skeleton is no great disadvantage because of the
non-predatory habits of this species, which places
no premium on speed and agility.
The most significant feature in the panda skeleton
is a generalized, increase in the quantity of compact
bone. This probably has an extremely simple genetic
base. The increased thickness of compacta is advan-
tageous only in the skull.
DAVIS: THE GIANT PANDA
123
Many proportions in the skeleton of the panda
and to a lesser extent in the skeleton of bears
are a mixture of those seen in bipedal, in burrow-
ing, and in graviportal forms. In part these pro-
portions are mutually contradictory adaptations
associated with bipedalism are not the same as
those associated with graviportalism and in part
they are not contradictory, since adaptations for
withstanding anteroposterior thrust are similar in
bipedal and burrowing forms. Still other propor-
tions in the panda, particularly in the limbs, cannot
be reconciled with any mechanical requirements,
and appear to represent disharmonious relations
of the "subordinated gene effect" variety. The
fact is that the panda does not burrow, it is bi-
pedal only to the extent that, like many other
mammals, it occasionally stands erect for short
periods, and it is not heavy enough to qualify as
graviportal. These facts show that the ill-assorted
features distinguishing the postcranial skeleton of
the panda from that of Ursus are not truly adap-
tive, and that where they agree with conditions
that presumably are adaptive in other specialized
forms (bipedal, fossorial, graviportal) such agree-
ments are either fortuitous or based on something
other than functional demands.
Thus we are confronted with a highly modified
and strongly adaptive skull associated with a con-
siderably modified postcranial skeleton in which
the departures from the "ursid norm" appear to
be completely non-adaptive, even inadaptive to
the extent of producing a disharmonious organism.
From what is known of the genetics of acromegaly,
achondroplasia, and other pathological conditions
of the skeleton in dogs and mice (Stockard, 1941;
Griineberg, 1948) the most economical interpreta-
tion, consistent with all known facts, of the syn-
drome of non-adaptive features in the skeleton of
Ailuropoda is that they are associated pleiotropi-
cally with the one definitely adaptive feature. It
is even highly probable that the whole complex
has a very simple genetic base.
The persistence of such morphological dishar-
monies in a natural population is unusual but not
unique, and might in fact be anticipated in highly
specialized forms whose adaptive niche places a
low premium on all-around mechanical efficiency.
Similar disharmonies are clearly evident in the
hyenas, which like Ailuropoda are highly special-
ized for masticatory power but do not need speed
or agility either to escape from enemies or to cap-
ture prey.
It is suggestive that bipedal, fossorial, and gravi-
portal mammals are all characterized by local
strengthening of the skeleton (i.e., by increase in
quantity of compacta). The changes in form and
proportions associated with such local strength-
ening are presumptively adaptive, and in some
instances it can be shown unequivocally that they
are the moments of resistance in the vertebral
column of bipedal forms, for example. In other
instances attempts at a functional explanation
have been unsuccessful; for example, pelvic archi-
tecture in bipedal and burrowing forms. In many
instances no functional explanation has even been
attempted; for example, limb proportions in gravi-
portal forms. If it can be demonstrated that cer-
tain features in the skeleton are correlated with
increased quantity of compacta rather than with
other functional requirements, then an association
between such features and a particular functional
requirement is merely a chance association. At-
tempts to read adaptive significance into such
associations are, of course, based on a false as-
sumption and can only lead to false conclusions.
The existence in the panda skeleton of numerous
ill-assorted conditions convergent with conditions
in bipedal, fossorial, and graviportal forms sug-
gests that such spurious correlations with func-
tional requirements may be more common than
has been assumed. Much more data are required
to prove this suggestion.
Numerous ill-assorted disharmonies in the post-
cranial skeleton of the panda are connected pleiotrop-
ically, as subordinated gene effects, with the increase
in quantity of compacta.
One other feature in the skeleton demands atten-
tion: the specialized and obviously functional ra-
dial sesamoid. It was concluded (p. 183) that all
that would be required to derive this mechanism
from the radial sesamoid of Ursus is simple hyper-
trophy of the bone. This symmetrical increase in
the dimensions of a single bone is quite a different
thing from the hypertrophy of the compacta seen
elsewhere in the skeleton. The localized remodeling
seen in the sesamoid surely has a specific genetic
base, as is strongly indicated by the "sympathetic"
hypertrophy of the tibial sesamoid. The parallel
and non-functional hypertrophy of the tibial sesa-
moid also indicates that the genetic mechanism is
a very simple one, perhaps involving no more than
a single gene.
The highly specialized and obviously functional
radial sesamoid has a specific, but probably very
simple, genetic base.
Disregarding any minor polishing effects of nat-
ural selection, aimed at reducing disharmonious
relations, it appears that the differences between
the skeleton of Ailuropoda and that of Ursus could
be based on no more than two gene effects. There
is, of course, no way of proving that the situation
actually was so simple, but mechanisms capable
124
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
of producing comparable eflfects on the skeleton
have been demonstrated experimentally in other
mammals. The alternative explanation numer-
ous small gene effects screened by natural selection
postulates a vastly more complex process, and
leaves unexplained the many clearly inadaptive
features in the skeleton. We could, of course,
assume that these several inadaptive features ap-
peared one by one during the evolution of Ailuro-
poda, and persisted simply because there was little
or no selection against them. But if each of these
is unconnected with any of the other gene effects,
then any selection pressure would have eliminated
them. Obviously there is some selection against
any inadaptive feature; no feature is truly adap-
tively neutral. Therefore it seems to me that
probability strongly favors a single gene effect as
the causal agent for all the hereditary differences
between the skeleton of Ailuropoda and Ursus,
except in the radial sesamoid.
The major features distinguishing the skeleton of
Ailuropoda from that of Ursus may depend on as
few as two gene effects. These are:
(a) Generalized hypertrophy of compacta.
(b) Specific hypertrophy of the radial sesamoid.
VOL CONCLUSIONS
1. The skeleton of Ailuropoda resembles the
skeleton of Ursus in all essential respects.
2. Many skeletal differences between Ailuro-
poda and Ursus are epigenetic to the bone tissue,
and therefore do not result from natural selection
on the skeleton.
3. The most significant feature in the panda
skeleton is a generalized increase in the quantity
of compact bone. This probably has an extremely
simple genetic base.
4. The increased thickness of compacta is ad-
vantageous only in the skull.
5. Numerous ill-assorted disharmonies in the
postcranial skeleton are connected pleiotropically,
as subordinated gene effects, with the increase in
quantity of compacta.
6. The highly specialized and obviously func-
tional radial sesamoid has a specific, but probably
very simple, genetic base.
7. Thus, the major features distinguishing the
skeleton of Ailuropoda from that of Ursus may
depend on as few as two genetic factors. These
are: (a) generalized hypertrophy of compacta; (b)
specific hypertrophy of the radial sesamoid.
DENTITION
I. DESCRIPTION
The classification of mammals has depended
more on the dentition than on any other single
feature of morphology. The teeth of the giant
panda have repeatedly been studied and discussed
in great detail (Gervais, 1875; Lydekker, 1901;
Bardenfleth, 1913; Gregory, 1936; McGrew, 1938).
These studies have led to the most divergent views
as to the homologies of the various cusps, and in-
ferences as to the affinities of Ailuropoda based on
such homologies. I conclude that the cheek teeth
of Ailuropoda are so modified from those of any
other known carnivore that interpretations based
on them have been largely subjective.
The dental formula of Ailuropoda is
If CI Pi M=42,
which is the primitive form for the recent Carni-
vora. The formula is the same in small species
of Ursus, but various additional teeth have been
lost in large species of Ursus and in other genera
of the Ursidae. In the Procyonidae and Ailurus
the third lower molar has disappeared, giving the
formula
U C{ Pi Mt=40.
The incisors are in no way remarkable in Ailu-
ropoda. As in carnivores in general, in both jaws
they increase in size from the first to the third.
As in Ursus (much less so, if at all, in other arc-
toids), the third incisor in both jaws is abruptly
larger than the second, and in the upper jaw is
less chisel-shaped and more caniniform than the
two more medial incisors. The third incisor is
relatively larger in Ailuropoda than in Ursus, and
is separated from the canines by a very short dia-
stema. The shortness of the diastema is the only
evidence of crowding in the anterior dentition.
The incisors are, of course, single rooted.
The six incisors in each jaw are closely crowded,
their combined occlusal surfaces forming an essen-
tially continuous, slightly arched, scraper or chisel
edge. The resulting tool, lying between and often
slightly in front of the canines, is one of the most
characteristic features of the dentition of the Car-
nivora.
The canines are more robust than in Ursus, in
both long and transverse diameters. Their rela-
tive length is almost identical in bear and panda,
however, and this gives the canines of Ailuropoda
a relatively stumpy appearance. In the unworn
dentition there is a vertical ridge on both anterior
and posterior surfaces of the upper canine, and on
the posterior surface only of the lower. Similar
ridges are seen in other arctoids (e.g., Procyon),
but not in Ursus. Ailurus, along with the pro-
cyonids Bossoncyon and Potos, has vertical grooves
on its canines. The phylogenetic and functional
significance, if any, of these surface sculpturings
is unknown.
The upper canine in Ailuropoda projects for-
ward at an angle of about 30. The same tooth
forms an angle of about 15 in Ursus, while in
other arctoids examined it does not deviate more
than a couple of degrees from the vertical.
The premolars increase in size from the first
to the fourth, as in all arctoids. The first premolar
is degenerate and peg-like in both jaws, and is
often missing. In size and structure it contrasts
sharply with the remaining premolars. The re-
maining three teeth are crowded, and in both up-
per and lower jaws P2 is rotated at an angle of
about 30 from the axis of the tooth row.
In the upper series, P'^ is tri-lobed, two-rooted,
and with no indication of internal (lingual) cusps.
P ^ is very similar to P \ except in size. The fourth
upper premolar, the upper carnassial of the Car-
nivora, has been the chief object of discussion and
speculation in the dentition of the giant panda.
It is the largest of the premolars, but is neverthe-
less considerably smaller than the two upper mo-
lars. The tooth exhibits five prominent cusps
arranged in two longitudinal rows. The three on
the labial side are considerably higher than those
on the lingual, with the central one the highest of
all. These have been homologized, from front to
rear, with the parastyle, paracone, and metacone.
The two cusps on the lingual side are regarded as
the protocone (anteriorly) and the hypocone (pos-
teriorly). There are no cingula. The tooth has
three powerful roots, arranged in the form of a
triangle. The anteriormost root supports the para-
125
126
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Paracone
MettKone
AtUero-uiternal cusp
Protocovid
Hypocotiid
Protoconid tii-
liypoconid
h h I,
Protoconid-
Hypoconid-
Fig. 68. Occlusal views of unworn right upper and left lower dentitions of Ailuropoda (XI).
style, the protocone, and the anterior half of the
paracone. The posteroexternal root supports the
metacone and the posterior half of the paracone.
The posterointernal root supports the hypocone.
Five cusps, occupying similar positions, are found
on the upper carnassial of Procyon and Ailurus.
The mode of origin of the Procyon crown pattern
from the primitive three-cusped shearing carnas-
sial is well known and documented by fossil mate-
rial (McGrew, 1938). Morphologically the crown
pattern of Ailuropoda is very similar to that of
Procyon, but the relation of the cusps to the roots
is quite different and essentially nothing is known
of the history of this tooth in the panda. The
form of the crown in Ailurus is like that of Pro-
cyon and Ailuropoda, and the relation of cusps to
roots is like that of Procyon, not like that of Ailuro-
poda. It has been assumed by Lydekker, Gregory,
and McGrew that the morphological similarity in
cusp arrangement between the raccoon and the
giant panda denotes homology and hence common
ancestry. Winge and Bardenfleth, on the con-
trary, argued that the different cusp-root relations
show that the similarity in crown pattern is the
result of convergence.
In the Ursidae, by contrast, P^ is degenerate by
normal carnivore standards. It is relatively and
absolutely small, abruptly smaller than the mo-
lars, and its crown usually bears only three cusps:
the paracone, metacone, and protocone; in small
individuals of Ursus (e.g., U. americanus) there
may be a minute parastyle. The relation of cusps
to roots is identical with Ailuropoda.
The lower premolars are simpler and more uni-
form than the upper, but otherwise follow the
trend of the latter closely. As in the upper jaw,
the first premolar is small and peg-like and con-
trasts sharply with the following teeth. It is often
DAVIS: THE GIANT PANDA
127
missing. Pj,, like its antagonist, is rotated at an
angle of about 30 from the axis of the tooth row.
P , increase in size from front to rear, but P,
* is much smaller than the following M,. All are
trilobed, with three conical cusps in series along
the axis of the tooth. P^ has a small postero-
internal cusp, sometimes subdivided into several
f small tubercles. Thus the posteriormost part of
the lower premolar series is slightly broadened.
All the lower premolars, except Pj, are two-rooted.
The upper molars are enormous and richly
cuspidate, dominating the entire upper tooth row.
They are abruptly and conspicuously larger than
the upper premolars, and are closely crowded.
M ' is almost square, slightly broader than long.
It bears two prominent conical cusps, the para-
cone and the metacone, on the labial side. Lin-
gually and directly opposite these there is a second
pair of smaller and lower cusps, the protocone and
hypocone. A third pair of poorly defined cusps is
situated in the valley between the outer and inner
rows of cusps; the homology, if any, of these cusps
is unknown. The internal border of the tooth
forms a broad shelf-like cingulum whose occlusal
surface is very regularly serrate. M^ is divided
into two subequal parts, a trigonid anteriorly and
a large talonid posteriorly. The anterior part of
the tooth is very similar to M Mn form and arrange-
ment of cusps and cingulum. The occlusal surface
of the talonid is richly tuberculate, with a long
blade-like cusp medially (immediately behind the
protocone, and perhaps representing an elongate
hypocone) and a narrow cingulum. There are
three roots on M ' , two lateral and one medial, as
is typical of the Carnivora. The medial root is
greatly expanded anteroposteriorly, and is partly
divided by a groove into two pillars that lie be-
neath the two medial cusps. M'-, in addition to
the usual three roots, has a fourth large root sup-
porting the talon.
The upper molars of Ailuropoda are fundamen-
tally similar to those of Ursus, but they differ in
two seemingly important respects: their relatively
larger size, especially their greater breadth; and
the rich development of secondary tubercle-like
elevations. The extinct European cave bear, Ur-
sus spelaeus, reached a larger size than any other
known member of the genus Ursus, and hence had
the largest molars. It is therefore extremely sug-
gestive that the molars of the cave bear, while
retaining their ursid outlines, exhibit the same rich
development of secondary cusps and tubercles as
is seen in the giant panda. The similarity of the
molars in these two forms, except for the broaden-
ing of the crown in Ailuropoda, is quite astonishing.
The lower molars are simpler and less broadened
than the upper. M^, the lower carnassial, has
lost its sectorial character and is quite similar to
the corresponding tooth in both Ursus and Pro-
cyon. There are five cusps, which retain the prim-
itive arrangement (fig. 68). The facing slopes of
the entoconid and hypoconid exhibit low tubercle-
like elevations similar to the medial row of cusps
on M ' , but these are lacking between the proto-
conid and metaconid. There is a poorly defined
cingulum externally. M ^ is more tuberculate than
Mj, and the cusps are less sharply defined. The
paraconid, which is prominent on Mj, cannot be
identified with certainty on M ^ . This cusp is often
almost completely coalesced with the protoconid
in Ursus. It is also associated with the proto-
conid in Ailurus, but there is no indication of it
in Procyon. M., has a rounded triangular outline
in Ailuropoda, and the cusps are almost completely
obliterated on its flattened crown. The occlusal
surface, which opposes the talon of M'^, is thrown
up into a complex pattern of low tubercles. The
outline and crown pattern of M 3 in Ailuropoda are
quite different from the more typically molariform
Mg of Ursus. It is noteworthy, however, that
Rode (1935, pi. 7) illustrates, as "abnormal" ex-
amples, several lower third molars of the gigantic
Ursus spelaeus and these are almost exactly like
M., of Ailuropoda.
II. DISCUSSION OF DENTITION
It has long been the custom of systematists to
regard individual teeth, and even individual cusps,
as the basic units of the dentition. Thus, by im-
plication, these units are construed as individually
gene-controlled and therefore subject to individual
selection. The tooth as a whole, to say nothing
of the dentition as a whole, would then be a mosaic
of individually derived elements, each of which
survives or perishes according to the way in which
it functions in the dental activities of the animal.
Similarities between adjacent teeth are ascribed
to convergence resulting from selection. Such a
view naturally places great emphasis on "homol-
ogies" between cusps and similar elements as in-
dicating affinities between animals. Furthermore,
the minute structure of each tooth is perforce
directly correlated with function.
In practice, the teeth are minutely scrutinized
and compared, element by element, for similari-
ties in structure. Identity or near identity in
architecture is construed as an infallible indicator
of relationship, and vice versa. Certain teeth (P^
in the Carnivora) are often assumed to be better
indicators of affinities than others. This method
has worked in the majority of cases because in
128
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
closely related forms the dentitions, like other
morphological features, usually are closely similar.
There is a considerable residue of forms with spe-
cialized dentition, however, whose relationships
cannot be resolved by any amount of peering at
the teeth as discrete entities. As Bateson re-
marked more than half a century ago, "the attri-
bution of strict individuality to each member of
a repeated series of repeated parts leads to ab-
surdity." No better example of the limitations of
this method could be asked than the giant panda.
On the basis of a mechanical point-by-point
comparison, the teeth of Ailuropoda are in some
respects more similar to the teeth of the Procy-
onidae than to those of the Ursidae. The whole
premolar series is strikingly degenerate in the
bears. Pl-3 are peg-like vestiges, often missing in
part. Even P* (the carnassial), normally the larg-
est tooth in the upper battery in carnivores, is
greatly reduced in all bears. In Ailuropoda, in
striking contrast, only PI is degenerate and the
remaining premolars are robust functional teeth.
P^ is large, with five well-formed cusps occupying
the same relative positions on the crown as they
do in Procyon and Ailurus (though they are dif-
ferently related to the roots). On the other hand,
the molars of Ailuropoda are far more bear-like
than procyonid-like, especially in the presence of
a large talon on M- and in the retention of M.,,
which is lacking in the Procyonidae. It was the
opinion of Lydekker, Gregory, and McGrew, how-
ever, that the premolar features are "more im-
portant" than the molar.
Two recent concepts have greatly changed our
ideas of the evolution of dentitions. Structures
such as teeth or vertebrae are serially repeated
(homeotic) elements. It has been found that such
structures are at least partly controlled by genes
exerting a generalized effect over a region com-
prising several adjacent elements, rather than on
each isolated element. This is the field control
concept. Sawin (1945, 1946) and Sawin and Hull
(1946) have so interpreted hereditary variations in
vertebral formula in rabbits. Butler (1939, 1946)
has applied the field concept to the teeth of mam-
mals, arguing that they are homeotic structures
that have evolved as parts of a continuous mor-
phogenetic field rather than as isolated units, and
that a common morphogenetic cause must have
acted on more than one tooth germ to account for
the close similarity between adjacent teeth. The
second concept is that of differential growth, which
was developed chiefly by Huxley (1932). Accord-
ing to this theory, now voluminously documented,
various structures may have a different growth
rate from that of the organism as a whole. Thus,
with increase in the size of the organism during
phylogeny, structures may attain a relative size
or degree of differentiation that is not directly
determined by the action of selection on the struc-
ture itself. The classic examples of the mandibles
of lucanid beetles and the antlers of deer are well
known, but it is not so well understood that this
principle may apply also to the teeth of mammals.
How do these concepts relate to the dentition
of Ailuropoda'! In the primitive carnivore den-
tition, as represented hy Canis, the dental gradient
of the upper cheek teeth centers in P' and M',
falling off steeply on either side of this center.
More specialized carnivore dentitions exhibit a
shifting of this center anteriorly or posteriorly
along the tooth row, and expansion or contraction
of the center to embrace one or several teeth
(fig. 69). The Ursidae differ from other Carni-
vora in that the center lies wholly in the molar
region, falling off abruptly at the boundary be-
tween molars and premolars. The molar empha-
sis is further reflected in the conspicuous posterior
extension of M- in the form of a large talon. In
Ailuropoda the whole premolar- molar battery has
been secondarily enlarged, but there is still the
same molar emphasis as in the bears. The dental
gradient is quite distinctive and different from
that of the Procyonidae.
Enlargement in Ailuropoda begins abruptly at
the boundary between the first and second pre-
molars; the teeth anterior to this line (first premo-
lar, canine, and incisors) are no larger than in
Ursus, whereas teeth posterior to the line are all
enlarged to approximately the same degree. These
correspond almost exactly to the canine and in-
cisor fields and the molarization field, respectively,
of Butler. An astonishingly close parallel to this
condition is seen in the fossil anthropoid Paran-
thropus robustus (Broom and Robinson, 1949), in
which the premolar-molar series is so much and
so abruptly larger than the canine-incisor series
that it is difficult to believe they belong to the
same individual.
The data of Rode (1935) on the dentition of
fossil and recent bears present a clear picture of
changes directly correlated with skull size in the
genus Ursus. Such changes are the result of dif-
ferential growth rather than of direct selection on
the dentition, and are only secondarily (if at all)
related to the functioning of the teeth. The pre-
molar dentiton is reduced in all members of the
genus, no doubt as a result of selection, but de-
terioration becomes progressively more pronounced
with increased skull size. In small forms ( Ursus
americanus) the formula is typically Pi; among
the medium-sized species it is f in U. arctos and
DAVIS: THE GIANT PANDA
129
Canis
Felis
Mustela
Procyon
Ailurus
Ursiis
Ailuropoda
Fig. 69. Upper cheek teeth of representative carnivores to show varying gradients in the premolar-molar field.
f in U. horribilis, but in the huge U. spelaeus it
is { or even ^.' Thus there is an inverse correla-
tion between skull size and premolar development
in Ursus, and reduction of the premolars is a fea-
ture of the growth pattern of this genus, its ex-
pression becoming increasingly pronounced with
increased skull size. It is probable, furthermore,
that the growth pattern was established early in
bear phylogeny, in animals of relatively small size,
in adapting the primitive carnivore dentition to
the requirements of the bear stock. The almost
total suppression of the premolars in large species
would then be merely an expression of the gi'owth
pattern of the bear stock, a direct result of selec-
tion for larger size, not of selection on the dentition
itself. If an individual American black bear grew
' The Alaskan brown bear (Ursus gyas), with a basal skull
length up to 405 mm., may rival U. spelaeus in size. The
cheek teeth of gyas are the same absolute size as in the
grizzly, however, showing that a new and different factor
(probably resulting from direct selection on the dentition)
has affected the teeth in gyas. The premolar formula is
typically f .
to the size of a cave bear, we should expect its
pi'emolars to resemble those of a cave bear.
With respect to the molars, Rode's data show a
direct correlation between tooth size and elabora-
tion of the crown sculpture in the form of second-
ary wrinkles and tubercles. The cingula also
become wider and better defined with increased
tooth size. Both reach a peak in Ursus spelaeus.
Thus, elaboration of the molar crown pattern is
directly correlated with tooth size, and is an ex-
pression of the growth pattern of the bear stock.
The condition seen in U. spelaeus results from the
absolutely larger teeth, not from selection on the
teeth themselves.
The consequences of differential growth thus re-
veal two significant features of the dentition of
bears. These probably could not have been de-
tected, and certainly could not have been verified,
at the stage when they were under the active in-
fluence of natural selection. The later effects seen
on larger individuals, by exhibiting the results of
the pattern in exaggerated form, leave little doubt.
130
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
The two ursid features are: (1) almost total shift
of emphasis to the molar region of the cheek-tooth
field, with the great talon suggesting a tendency
to carry the center as far posteriorly as possible,
and (2) elaboration of the crown sculpturing of
the molars.
The basal skull length of Ailuropoda is slightly
less than that of the American black bear. The
molar teeth are disproportionately large, their ab-
solute length agreeing with the much larger gizzly.
But the whole tooth row of Ailuropoda is also
enormously broadened, and the molars equal (M-)
or exceed (M') those of the cave bear in width.
The broadening affects the premolars as well as
the molars (i.e., it extends over the whole cheek-
tooth field), and the disparity between premolar
and molar size is not as obvious as in the bears.
Nevertheless the molar dominance is still evident
in Ailuropoda.
Broadening of the premolars in Ailuropoda is
associated with the development of an internal
row of cusps, as it is in Procyon and Ailurus, the
other two arctoids in which the cheek teeth are
broadened. These cusps are, of course, conspicu-
ously wanting in the reduced premolars of Ursus.
Now, their presence in Ailuropoda may (1) indi-
cate affinities with the procyonids, or (2) be an
expression of the common genetic background of
the arctoid carnivores. As will appear in the se-
quel, there can be no doubt of the ursid affinities
of the giant panda, and therefore the second of
these alternatives is correct. The internal row of
cusps in Ailuropoda is the result of broadening
of the premolars.
The surface sculpturing of the molars is much
more elaborate in Ailuropoda than in the small
and medium-sized bears, but it is almost identical
with that of the gigantic Ursus spelaeus. If, as
pointed out above, elaboration of sculpturing is a
function of absolute tooth size in the bear stock,
then this is exactly what we should expect in the
huge molars of Ailuropoda. Any relation between
the "bunodont" character of the molars of Ailu-
ropoda and its diet is fortuitous. It is only the
enlargement and broadening of the teeth that are
so correlated.
Thus, given the morphogenetic pattern of the
bear stock, only two (perhaps only one) important
new factors have appeared in Ailuropoda. In the
ursid stock the morphogenetic field is concentrated
in the molar region, with the premolar field essen-
tially vestigial. In Ailuropoda the ursid pattern
has been further altered by two' simple morpho-
genetic factors: (1) secondary enlargement of the
whole cheek-tooth field, and (2) secondary broad-
ening of the whole field. Note that both of these
factors affect the cheek-tooth field as a whole (ex-
cept PI, which is vestigial), with no indication of
a gradient that did not already exist in the bears.
It is these two factors that represent adaptation
in the dentition of Ailuropoda, and not the de-
tailed architecture of each individual tooth.
III. CONCLUSIONS
1. In Ursus the expression of the dentition is
a function of skull and or tooth size. Elements in
the premolar field degenerate progi'essively with
increasing skull size among the species of Ursus,
whereas the molar crown pattern becomes increas-
ingly elaborate as absolute tooth size increases.
2. The dentition of Ailuropoda is an ursid den-
tition in which all elements in the premolar-molar
field (except PI) have become uniformly much en-
larged and broadened. The result is a disharmo-
nious relation between skull and dentition, which
is reflected in the displacement of P2.
3. The molar crown pattern of Ailuropoda
closely resembles that of the gigantic Ursus spe-
laeus. The molar crown pattern of Ailuropoda is
therefore a function of tooth size, not of selection
for a particular pattern.
4. Successive disappearance of premolars, which
accompanied increased skull and or tooth size in
Ursus, is not evident in Ailuropoda, although the
ursid proportions between premolar and molar size
are retained.
5. In Ailuropoda, selection was for increased
cheek-tooth size. Selection operated on the mor-
phogenetic field of the cheek-tooth battery as a
whole rather than on individual units. The result
is that all units in this field are enlarged to the
same relative degree.
6. The genetic mechanism behind this trans-
formation is probably very simple and may in-
volve a single factor.
' Increased tooth length may, of course, be merely a sec-
ondary result of broadening, in which case only a single new
factor would be involved.
ARTICULATIONS
Descriptions of the joints of mammals other
than man are very few, and are incomplete for
even the common domestic mammals. This is
unfortunate, since no mechanism the mastica-
tory apparatus or the hand, for example can be
understood unless the structure and functioning
of the joints are known. Comparative arthrology,
the comparative anatomy of the joints, cannot be
said to exist as an organized body of knowledge.
No attempt is made here to describe all the
joints of the giant panda. Those forming parts
of mechanisms that are much modified in Ailu-
ropoda the mandibular, wrist, and ankle joints
were studied in detail and compared with the
corresponding joints in the bears. A few other
joints, chiefly those important in locomotion, are
also described.
I. ARTICULATIONS OF THE HEAD
Mandibular Joint
The mandibular joint is a sliding hinge joint, as
in all carnivores. The two joint surfaces are very
closely congruent, as they are also in Ursus; they
are less so in some other carnivores. The joint in
Ailuropoda is not quite transverse, its axis in the
frontal plane forming an angle of 5 10 with the
transverse axis of the skull. This compares with
a range of 5-20 in a series of Ursus. In the trans-
verse plane the axis is depressed toward the mid-
line at an angle of about 10, compared with about
2 in Ursus. These deviations from the transverse
axis represent sectors of two circles, one in the
transverse and one in the frontal plane, whose
common center lies some distance in front of the
canines. They reflect the fact that the canines
interlock as they come into occlusion, checking
transverse movement at this point and causing
the canines to act as a point of rotation. Since the
canines are conical rather than cylindrical, the
actual point of rotation lies in front of the canines.
The mandibular joint is remarkable for its mas-
siveness, its relative size exceeding that of any
other carnivore. It is also displaced dorsally and
posteriorly relative to its position in Ursus. This
displacement increases the mechanical efficiency
of the jaw apparatus for crushing and grinding
(p. 69).
The articular capsule is a close-fitting sac, heavy
posteriorly but much thinner anteriorly, where it is
intimately associated with fibers of the temporal
muscle. The capsule is attached to the margin of
the mandibular fossa all around, and to the mar-
gin of the articular surface on the capitulum of the
mandible. There is no thickening at the lateral
end corresponding to the temporomandibular liga-
ment of human anatomy.
The articular disk is almost paper-thin and is
imperforate. It increases slightly in thickness from
anterior to posterior and is not notably thinner
at the center than at the periphery. The disk is
firmly attached to the capsule throughout its en-
tire periphery, and is more tightly attached to the
fossa than to the condyle. None of the external
pterygoid fibers insert into it.
A single ligament is associated with the man-
dibular joint (fig. 70). This apparently represents
the stylomandibular ligament combined with the
posterior end of the sphenomandibular ligament;
in Ursus these two are separate and distinct and
attach at the normal sites. The ligament is a band
about 5 mm. wide, attached anteriorly to the an-
gular process of the mandible. From this attach-
ment it runs posteriorly, dorsally, and medially
beneath the outer end of the postglenoid process.
Here it bifurcates, one branch going to the inferior
surface of the bony auditory meatus (the normal
attachment of the sphenomandibular ligament)
and the other to the inferior surface of the carti-
laginous auditory meatus (the normal attachment
of the stylomandibular ligament). The absence
of the anterior part of the sphenomandibular liga-
ment, which normally attaches at the entrance to
the mandibular foramen, is probably associated
with the great size of the postglenoid process.
Movement in the mandibular joint consists, as
in all carnivores, of two components: hinge move-
ment around an approximately transverse axis, in
which the cylindrical head rotates in the trough-
like fossa; and sliding movement, in which the
head shifts transversely in the fossa. These two
movements are combined into a spiral screw move-
131
132
FIELDIAXA: ZOOLOGY MEMOIRS, VOLUME 3
Proe. augularit
mandibulat
Capsula articularif
Prof, mastoideuf
Meatus acusticus ext.
CorpMS monuHbulat
M. pter\-goid. int.
Capsula articularU
Ljg. stytomandibulare
sphenomandibulare
Hamulus pterfgoidens
Proe. posi- glenoid.
Fig. 70. Right mandibular joint of Ailuropoda, external view.
ment, as is evident from the wear surfaces on the
teeth. Measured on the dr>- skull, the lateral com-
ponent amounts to about 6 mm. after the cheek
teeth first begin to come into occlusion. The cor-
resix)nding lateral component is about 3 mm. in
a specimen of Ursiis aretos.
In summary-, the mandibixlar joint of Ailuro-
poda differs from that of I'rsus chiefly in being
larger and more robust, and in being displaced
dorsally and posteriorly. These are all directly
adaptive modifications. They can scarcely be
attributed to extrinsic factors, but probably rep-
resent the results of selection operating on intrinsic
(hereditan.-) factors. It is even plausible that the
increase in quantity of bone tissue in the skull as
a whole reflects the generalized working of the
morphogenetic machiner>- whereby increased size
of the bony elements of the mandibular joint was
effected.
II. .\RTICULATIOXS OF THE FORE LEG
A. Shoulder Joint
The shoulder joint is an extremely simple joint,
as it is in all mammals that lack a clavicle. The
only ligament is the loose articular capsule, and
consequently the joint is held in position solely by
muscles. .\s pointed out by Baum and Zietzsch-
mann for the dog, the powerful tendon of the in-
fraspinatus laterally, and that of the subscapularis
medially, functionally represent collateral liga-
ments of the shoulder joint. In addition to their
function of retaining the joint in position, these
tendons must also tend to limit adduction and
abduction of the humerus, and thus to i-estrict
movement to a pendulum-like flexion and extension.
The glenoid cavity of the scapula is remarkable
for its narrowness in comparison with other carni-
vores. The articular surface of the head of the
DAVIS: THE GIANT PANDA
133
humerus, in contrast, is broader than in other car-
nivores. The fibrous glenoid lip is inconspicuous
except along the posterior border of the glenoid
cavity, where it projects a couple of millimeters
beyond the edge of the bone.
The articular capsule is a loose sac enclosing
the shoulder joint on all sides. It extends from
the prominent rough surface around the margin
of the glenoid cavity of the scapula, to the head
of the humerus. On the humerus the capsule is
attached to the roughened area at the periphery
of the head. In the intertubercular area it is pro-
longed distad into the intertubercular sheath
that encloses the tendon of the biceps.
The posterior (superficial) fibers of the triceps
medialis separate from the anterior (deep) fibers
at their origin, and arise from the inferior surface
of the capsule instead of from bone. Contraction
of this muscle would consequently exert traction
on the capsule. A very few of the posteriormost
tendon fibers of the triceps lateralis are also at-
tached to the joint capsule.
B. Elbow Joint
The elbow joint (figs. 71, 72) depends for its
strength and security on bony structures rather
than on the number, strength, or arrangement of
its ligaments, as is the case with the knee. In the
giant panda and bears the elbow joint is a screw
joint rather than a simple hinge joint as in other
carnivores. The spiral trough formed by the me-
dial half of the trochlea (fig. 49) forces the ulna to
travel medially 5 mm. or more as the elbow is
flexed. With the foot in the normal position of
pronation, this would throw the foot medially as
the elbow is flexed, and would account, at least in
part, for the rolling motion characteristic of the
fore feet in bears and the giant panda.
The capsule is a large and capacious sac to
which the collateral ligaments are inseparably
united. The supinator and a small part of the
abductor pollicis longus muscles arise directly from
the capsule. The bony attachments of the capsule
are as follows: (1) on the humerus it encloses the
vestigial coronoid fossa anteriorly and the ole-
cranal fossa posteriorly; laterally and medially it
attaches to the sides of the trochlea and the distal
ends of the epicondyles; (2) on the ulna it attaches
to the edges of the semilunar notches; (3) on the
radius it attaches just distad of the articular facet.
The lateral collateral ligament arises from
the lateral epicondyle and runs distad across the
radiohumeral articulation. At the annular liga-
ment it is interrupted by the origin of the supi-
nator muscle, beyond which it continues distad
to its attachment on the anterolateral surface of
the radius about 30 mm. below the head. A prom-
inent scar marks its radial attachment. There are
two lateral ligaments in the dog (Baum and
Zietzschmann) and cat (Reighard and Jennings),
one going to the ulna and the other to the radius.
The medial collateral ligament is stronger
and better marked than the lateral ligament. On
the humerus it is attached to the area in front of
the medial epicondyle. The nearly parallel fibers
pass across the joint and attach on the ulna in the
conspicuously roughened area immediately distad
of the semilunar notch. In both the dog and the
cat the medial ligament is double, consisting of
radial and ulnar heads.
The oblique ligament is a slender band run-
ning diagonally across the anterior (flexor) surface
of the lateral epicondyle. Distally it attaches to the
distal lip of the semilunar notch. In the dog the
oblique ligament divides distally to embrace the
tendons of the biceps and brachialis (Baum and
Zietzschmann). Parsons (1900) says it is absent
in Ursus, and Reighard and Jennings do not men-
tion it in the cat.
C. Union of the Radius with the Ulna
The radius and ulna are united at three places:
a proximal and a distal radioulnar articulation,
and a mid-radioulnar union via the interosseous
ligament.
The proximal articulation is composed of the
radial notch of the ulna and the smooth circum-
ference of the head of the radius that rotates in it.
Two ligaments are special to the joint. The lat-
eral transverse ligament (fig. 71) is a short diag-
onal band extending from the annular ligament
just below the lateral collateral ligament to the
border of the semilunar notch immediately behind
the radial notch. This ligament is absent in the
dog (EUenberger and Baum, 1943) but is present
in the bears. The annular ligament of the ra-
dius is a well-defined band of strong fibers about
15 mm. wide, encircling the head of the radius.
It forms about 60 per cent of a ring, which is com-
pleted by the radial notch of the ulna. The an-
nular ligament is thickest over the notch in the
head of the radius. It is strongly attached at
either end to the margins of the radial notch, and
is much more feebly attached by loose fibers to the
neck of the radius below the epiphyseal line.
Since the head of the radius is elliptical in out-
line, it acts as a cam and imparts an eccentric
motion to the radius during movements of prona-
tion and supination. The cam action can easily
be felt through the annular ligament when the
radius is rotated on a ligamentary preparation.
This eccentric motion has the effect of permitting
lumerus
Lag. transversum laterale
Capsula articularis
Fig. 71. Right elbow joint of Ailuropoda, bent at right angle, lateral \-iew. Foreann halfway between pronation and
supination.
\Ulna
Fig. 72. Right elbow joint of Ailuropoda, bent at right angle, medial view. Forearm halfway between pronation and
supination.
134
J
DAVIS: THE GIANT PANDA
135
a certain amount of rotation of the radius witiiout
stretching the interosseous ligament.
The range of movement in the proximal radio-
ulnar articulation appears to be severely limited
in Ailuropoda. The pronation-supination range
was about 40 (compared with 120-140 in man)
on a ligamentary preparation when the radius was
ments lying just distad of the radioulnar articula-
tion. The dorsal radioulnar ligament (fig. 73)
is a rope-like band attached at one end to a pit-
like depression on the neck of the styloid process
of the ulna, between the radioulnar articulation
and the head. The other end attaches to the ra-
dius immediately below and in front of the radio-
Lig. radioulnaris dors.
Bursa m. ext. y-<^ -^
carpi ulnaris ^^ ~ ^ ^t^
Comp;irtment for Radius ^facics artic. carpeae)
M. ext. dig. com.
Capsula articularis
Proc. styloideus ulnae
Lig. radiocarpi volari
Septum artic. (cut)
Fig. 73. Proximal articular surfaces of right antebrachiocarpal joint of Ailuropoda.
rotated by grasping its distal end and manipulat-
ing it by hand. Further rotatory movement was
checked by the capsule of the proximal radioulnar
articulation, by the interosseous ligament, and by
the distal radioulnar ligaments.
The interosseous ligament (figs. 71, 72) is a
thick tract of glistening fibers extending between
the ulna and the radius except for the proximal
quarter of the interosseous space. The ligament
is heaviest in the middle third of the interosseous
space, becoming thin and almost membranous in
the distal third. Most of the fibers run diagonally
distally from the radius to the ulna, but on the
anterior surface a large group of proximal fibers
runs in the opposite direction. The interosseous
ligament is so heavy that it binds the ulna and
radius firmly together, permitting very little move-
ment between them.
Nothing comparable to the oblique chord of
human anatomy is present in Ailuropoda.
The distal radioulnar articulation (fig. 73) op-
poses a flat, almost circular surface on the radius
to a slightly convex, almost circular surface of the
ulna. The surface on the radius is parallel to
the midline of the radius (which curves toward the
ulna in its distal quarter), whereas the surface on
the ulna lies at an angle of about 45 to the long
axis of the ulna. The articulation is enclosed in a
capsule. This articulation, which closely resem-
bles that of Ursus, permits the distal end of the
radius to roll around the ulna in a limited arc.
In Ailuropoda the distal ends of ulna and radius
are held together by two strong transverse liga-
ulnar articulation. The volar radioulnar liga-
ment attaches at one end to the neck of the styloid
process and at the other to the border of the distal
articular surface of the radius, near the radioulnar
articulation. It lies mostly deep to the volar radio-
cai-pal ligament.
D. Hand and Intercarpal Joints
The range of movement of the hand as a whole
is very great in primitive carnivores. All the pos-
sible angular movements rotation, flexion and
extension, and abduction and adduction, together
with combinations of these can be carried out.
One of the most important and extensive of these
movements, rotation (inversion and eversion), is
scarcely a function of the hand joint, but results
almost entirely from movements of pronation and
supination of the forearm and rotation in the
shoulder joint.
The essential hand joint for movement of the
hand as a whole is the antebrachiocarpal joint (the
radiocarpal joint of human anatomy). In all
the other joints movement is extremely restricted,
consisting only of a slight gliding of one bone upon
another, which serves to give elasticity to the
carpus. In a ligamentary preparation of Ailuro-
ropoda, movement in the intercarpal and carpo-
metacarpal joints is almost non-existent, whereas
in a similar preparation of the bear Tremardos
there is considerable movement in these joints,
particularly in the direction of adduction and ex-
tension.
Ailuropoda
RADIAL
Add.
ULNAR
Tremarctos
Anterior View (adduction - abduction)
Abd.
Ext.
Flex.
-12
Ext.
Lateral View (flexion - extension)
Flex.
Fig. 74. Diagrams showing ranges of movement in the left antebrachiocarpal joint in ligamentary preparations of a
giant panda and a spectacled bear. See text.
136
DAVIS: THE GIANT PANDA
137
Antebrachiocarpal Joint
A double joint, consisting of the radius-scapho-
lunar articulation medially, and the ulna cunei-
form and pisiform articulation laterally. The joint
cavity is partly divided into radial and ulnar com-
partments by an incomplete septum of fibro-
cartilage (fig. 73). This septum, the "triangular
fibro-cartilage" of Parsons, is attached proximally
to the radial side of the neck of the styloid process
of the ulna; distally it passes into the notch be-
tween the scapholunar and cuneiform and attaches
to the scapholunar. Along its volar edge the sep-
tum is continuous with the joint capsule, thus
closing off the radial and ulnar compartments, but
dorsally it stops abruptly at the level of the dorsal
radioulnar ligament, leaving the radial and ulnar
compartments in communication with each other.
The distal articular surface on the radius is
broader anteroposteriorly than in Ursus, and lacks
the conspicuous saddle over the styloid process.
The opposing articular surface on the scapholunar
is smoothly ovate, lacking the depression into
which the saddle fits in Ursus, and is about a
third more extensive than the radial articular sur-
face. Thus this part of the joint is an almost per-
fect ellipsoid articulation, capable of extensive
movements of flexion, extension, abduction, and
adduction. Of these, only abduction is seriously
restricted by the styloid process of the ulna and
the ulnar collateral ligament, which also inhibits
rotation almost completely. Range of the other
movements is greatly facilitated by the disposition
of the antebrachiocarpal ligaments.
The ulnar-carpal part of the antebrachiocarpal
joint is notable for the extent and flatness of the
articular surface on the cuneiform-pisiform com-
plex. Instead of forming a socket into which the
styloid process of the ulna fits, as in Ursus, in
Ailuropoda there is an extensive articular area
over which the styloid process can wander. This
articular area faces laterally, and therefore cannot
transmit thrust from the carpus to the fore arm
as it does in Ursus. Thus this part of the ante-
brachiocarpal joint in Ailuropoda has the function
of steadying the radio-scapholunar part of the joint.
The following measurements of ranges of move-
ment in the antebrachiocarpal joint were made on
an embalmed adult panda and an adult spectacled
bear. All muscles and tendons crossing the carpus
were removed, but all ligaments were left intact.
The fore leg was immobilized and the manus ma-
nipulated from the distal end, the operator taking
care not to force the manus beyond its normal
limits or to induce movements in intercarpal or
carpometacarpal joints. Angulation was read off
directly on a protractor, two or mo;e readings be-
ing made for each position. The long axis of meta-
carpal 3 was used as the axis of the manus (see
fig. 74).
Ailuropoda Tremarctos
Abduction adduction 29 22
Abduction (from radial axis=0). . . 4 9
Adduction (from radial axis=0). . . 25 13
Flexion-extension 78 55
Flexion (from radial axis=0) 59 67
Extension (from radial axis=0) .... 19 12
These figures indicate that the position of the
manus in relation to the fore arm in the panda is
quite different, in both planes, from its position in
the bear. The axis of the radius is not the true
axis of the fore arm, but it is close enough to show
that in the "rest" position the hand of Ailuropoda
is adducted whereas that of Tremarctos is abducted,
and that the metacarpus is more strongly flexed in
Ailuropoda than in Tremarctos. The figures also
indicate that the range of movement in the ante-
brachiocarpal joint is greater in the panda than
in the bear, particularly movements of extension.
The figures confirm the statement of Lips that the
bears are incapable of extending the metacarpus
beyond the long axis of the fore arm.
Ligaments of the Carpus
The carpal ligaments have not been described
for any generalized carnivore. In the present
study the ligaments of an adult spectacled bear
{Tremarctos ornatus) were dissected, for compari-
son, at the same time as those of Ailuropoda. The
only significant differences were the presence in
Tremarctos of stout dorsal radiocarpal and radial
collateral ligaments. The absence of these liga-
ments in Ailuropoda contributes greatly to the
mobility of the antebrachiocarpal articulation, par-
ticularly to the range of dorsal flexion.
Antebrachiocarpal Ligaments
The volar radiocarpal ligament (figs. 73, 76) is a
thick flat band of fibers with a predominantly
transverse direction. It is attached medially to
the radius above the styloid process, and laterally
to the neck and base of the pisiform ; its deep sur-
face presumably attaches to the scapholunar and
cuneiform. The proximal border of this ligament
is thick and sharply defined; distally it continues
into the transverse carpal ligament.
The dorsal radiocarpal and radial collateral liga-
ments of human anatomy are absent in the panda.
Instead there is a roomy, tough-walled articular
capsule enclosing the radiocarpal articulation dor-
sally and laterally (fig. 73). The capsule attaches
to radius and scapholunar near the margins of their
articular surfaces.
Lig. carp)sesam(i
Tendo m. abd.
poU. longus
Lig. basal is
Fig. 75. Dorsal carpal ligaments of Ailuropoda.
Os pisijorme
Lig.
pisometacarpeum.
Lig. pisocuneiform.
lat.
Tuberc. ossis ameift
Tendo mm. inter ossei
Tuberc. ossis magmon.
Ligg-
carpometacarp.
vol.
Lig. radiocarpeum
volare
Lig. carpi transvereum
Tendo m. flex, carpi rod.
Tuberc. ossis scapholunaris
Tendo m. abd. polUcis
lonffus
lig. carposesamoideum
volare
Os sesamoid, rod.
\ ^^ Lip. carpo -
sesamoideum
transv.
Ligg. basium
interossea vol.
Fig. 76. Volar carpal ligaments of Ailuropoda.
138
DAVIS: THE GIANT PANDA
139
The ulnar collateral ligament of the wrist (fig. 75)
is a heavy band of fibers extending from the latero-
dorsal surface of the styloid process of the ulna to
the distal end of the pisiform, where it attaches
to a prominent scar on the posterior surface of
the bone.
Intercarpal Ligaments
The transverse carpal ligament (fig. 76) is an ex-
tensive tract of transverse fibers, continuous proxi-
mally with the volar radiocarpal ligament. The
band is cupped to form a trough for the tendon of
the deep digital flexors. Attachment medially is
to the ventral process of the scapholunar, laterally
to the base of the pisiform. Its deep surface pre-
sumably attaches to the ventral processes of the
magnum, unciform, and cuneiform.
The pisohamate ligament is a short band on the
lateral aspect of the carpus. It attaches to the
pisiform near the margin of the articular surface
of the cuneiform, and to the lateral surface of the
ventral process of the cuneiform.
A system of short dorsal intercarpal ligaments
(fig. 75) ties the carpal bones together. These are
all short bands passing across from one bone to
its neighbor.
Ligaments of the Pisiform Bone
Two ligaments connect the pisiform with the
cuneiform. A volar pisocuneiform ligament passes
from the volar surface of the pisiform to the volar
surface of the cuneiform, median to the tubercle.
It is inseparable from the pisometacarpal ligament
throughout most of its length. A short lateral
pisocuneiform ligament passes from the lateral sur-
face of the pisiform, directly beneath the articular
surface, to the tubercle of the cuneiform (fig. 76).
A strong pisometacarpal ligament (fig. 76) ex-
tends from the volar surface of the pisiform to
the base of the fifth metacarpal.
Carpometacarpal Joints
The distal surfaces of the distal row of carpals
present a composite articular surface for the four
lateral metacarpals. In Ursus and most other
carnivores the otherwise smooth contour of this
composite articulation is broken by a wedge-shaped
projection of metacarpal 2 that thrusts back be-
tween the trapezium and trapezoid. This wedge
is absent in Ailuropoda, and the transverse con-
tour of the composite joint is therefore uninter-
rupted. Otherwise the joint is similar to that of
Ursus. The proximal articular surfaces on the
metacarpals are convex dorso-ventrally, with a
very slight transverse concavity on metacarpals
2-4 that produces a modified saddle joint. The
saddle joint is most pronounced on metacarpal 4,
and is wanting on metacarpal 5.
The first metacarpal articulates with the tra-
pezium by a saddle joint. The transverse curva-
ture of the saddle is shallow, as in the lateral
metacarpals. It is relatively deeper in Ursus, in-
dicating a greater range of adduction-abduction
movement.
Carpometacarpal Ligaments
Volar carpometacarpal ligaments are associated
with digits 3, 4, and 5 but are wanting on digits
1 and 2 (fig. 76). These are short stout bands
arising from the deep surface of the tendinous
plate by which the digital adductors take origin
thus eventually attaching to the magnum and
unciform and inserting asymmetrically into the
metacarpals near their bases. The ligament to
digit 5 attaches to the radial side of the bone,
those to digits 3 and 4 to the ulnar side.
A short dorsal carpometacarpal ligament extends
between the base of each metacarpal and the dor-
sal surface of the adjoining carpal bone (fig. 75).
Carposesamoid Joint
The articulation between the radial sesamoid
and the scapholunar is a true diarthrosis, capable
of quite extensive movements of abduction and
adduction, but probably incapable of dorsal and
volar flexion. On a ligamentary preparation this
bone could be manipulated through a range of
about 20 of abduction-adduction, but was practi-
cally immobile in the direction of flexion-extension.
The radial sesamoid in Ursus has no such diar-
throdial articulation, but the bone occupies the
same positions relative to the scapholunar.
Ligaments of the Radial Sesamoid
Four strong and well-marked ligaments are as-
sociated with the radial sesamoid bone. A short
volar carposesamoid ligament (fig. 76) passes from
the volar surface of the tubercle of the scapholunar
to the volar surface of the sesamoid bone. A
broad lateral carposesamoid ligament (fig. 75) passes
from the lateral surface of the scapholunar tuber-
cle to the lateral surface of the sesamoid, where it
attaches proximad of the insertion of the tendon
of the adductor poUicis longus. A transverse carpo-
sesamoid ligament (fig. 76) passes from the lateral
(ulnar) surface of the sesamoid into the transverse
carpal ligament. On the dorsal side a dorsal basal
ligament (fig. 75) connects the base of the sesamoid
with the adjacent base of the first metacarpal.
In Tremarctos the ligaments of the radial sesa-
moid are similar to, but smaller than, those in
Ailuropoda.
140
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Lig. patellae
Lig. menisci med. ant
Lig. cruciatum ant..
Tuberculum
intercondyloid. med..
Meniscus med
Lig. cruciatum post..
Lig. menisci
lat. ant.
Capsula articularis
Meniscus lat.
Lig. menisci lat. post.
Bursa
Fig. 77. Joint structures on head of right tibia of Ailuropoda.
Review of Hand Joint
Parsons (1900) reviewed very briefly the major
carpal ligaments of the Carnivora in relation to
those of other mammals, and concluded that the
wrist joint in carnivores is modified to permit a
"moderate amount" of supination. Lips (1930)
described in great detail the structure and function-
ing of the hand joint in Ursus arctos in compari-
son with other arctoid carnivores, unfortunately
without considering the ligaments. Lips concluded
that the hand joint of Ursus represents a "univer-
sal" (we would say unspecialized) type among the
arctoid carnivores, capable of many-sided move-
ments.
The hand joint of Ailuropoda is very similar to
that of Ursus, but the panda has gone beyond the
bear in the range of movement possible in the ante-
brachiocarpal joint, particularly extension. This
is accomplished by extending and reshaping artic-
ular surfaces, and by eliminating or reducing liga-
ments that would restrict dorsal flexion. Such
minor remodeling reflects the action of the mus-
cles that operate these joints (largely the carpal
extensors and flexors), and demands little or no
morphogenetic action on the bones and ligaments
themselves. Even the diarthrodial joint of the
radial sesamoid requires only the well-known ca-
pacity of bone to produce true joints wherever
movement occurs.
in. ARTICULATIONS OF THE HIND LEG
A. Knee Joint
The knee joint (fig. 77) is an incongruent com-
pound joint involving the femur, the patella, and
the tibia. The incongruence between the roller-like
condyles of the femur and the relatively flat supe-
rior articular surface of the tibia is compensated
by the menisci. The internal ligaments of the knee
joint of the horse, cow, pig, and dog were described
by Zimmerman (1933). The structure of this joint
in bears and procyonids is unknown. [
The menisci are unequal in size; the medial
meniscus is larger than the lateral and its struc-
ture is typical. The lateral meniscus has a promi-
nent ridge on the femoral side that separates a
medial articular area from a lateral non-articular
area. The non-articular part of the meniscus ter-
minates posteriorly at the entrance to a large
bursa, which is situated above and immediately
behind the fibular articulation. Each meniscus
is attached to the capsule throughout its entire
circumference, and each is also held in place by
its own system of ligaments. Each meniscus is
tightly attached to the head of the tibia at one
end and more loosely attached at the other, which
gives to both a certain freedom of movement on
the tibial head.
The lateral meniscus is continued into a liga-
ment at each end. The anterior ligament passes
mesad beneath the anterior cruciate ligament, to
attach to the medial wall of the anterior intercon-
dyloid fossa; the posterior one runs mesad and
dorsad, to attach to the intercondyloid fossa of
the femur. The medial meniscus is continued into
a ligament only at its anterior end; the posterior
end is tightly attached to the medial lip of the pos-
terior intercondyloid fossa. The anterior end of
the medial meniscus has no direct attachment to
DAVIS: THE GIANT PANDA
141
the tibial head; it is continued into a powerful
ligament that passes across immediately in front
of the anterior cruciate ligament to attach to the
anterior intercondyloid fossa in the area in front
of the lateral condyle, laterad of the attachment
of the anterior cruciate ligament. There is no
transverse tract uniting the menisci anteriorly,
corresponding to the transverse ligament of human
anatomy; Zimmermann states that this tract was
demonstrable in 94 per cent of the dogs that he
studied.
The cruciate ligaments are strong and rope-
like. The anterior cruciate ligament is attached
to the medial half of the anterior intercondyloid
fossa of the tibia, near the medial intercondy-
loid tubercle. It runs upward, backward, and
slightly laterad to the medial surface of the lateral
condyle of the femur, where it attaches. The pos-
terior cruciate ligament is considerably longer than
the anterior. It attaches to the tibia on a promi-
nence at the extreme posterior end of the posterior
intercondyloid fossa. From here it passes upward
and nearly straight forward, crossing the posterior
horn of the medial meniscus, and attaches to the
femur in the medial half of the intercondyloid fossa.
The only significant difference in the internal
ligaments of the knee joint between Ailuropoda
and the mammals described by Zimmermann is
the less tight fixation of the menisci, especially the
medial meniscus, in the panda. The resulting
greater freedom permits more extensive pronation
and supination in Ailuropoda.
B. Ankle Joint
The essential joints for movements of the foot
as a whole in the primitive carnivore are the upper
ankle joint, the transverse tarsal joint, and the
lower tarsal joint. Each of these joints is primarily
involved in a particular movement. In the upper
ankle joint, movement is a hinge movement in the
sagittal plane (flexion and extension of the foot).
In the transverse tarsal joint, movement is rota-
tion around the longitudinal axis of the foot (in-
version and eversion of the foot). In the lower
ankle joint, movement is an oblique gliding be-
tween the astragalus and calcaneus (largely ab-
duction and adduction of the foot) . None of these
joints acts entirely independently of the others,
and only the upper tarsal joint is confined to a
single fixed axis. The resulting combined move-
ments are extremely subtle and complex.
The small bones of the distal tarsal row are
probably mechanically unimportant. They func-
tion chiefly to break shocks and to increase the
general flexibility of the foot.
Upper Ankle Joint (talo-crural)
A perfect hinge joint between tibia and fibula
proximally and astragalus distally. Axis runs trans-
versely through trochlea of astragalus. Movement
is restricted to dorsiflexion and plantar flexion of
the foot.
Lower Ankle Joint (subtalar)
An incongruent gliding joint between astragalus
and calcaneus. No definite axis can be fixed; Fick
called the movement in this joint in man a "com-
promise" movement consisting of the summation
of successive rotations around a great number of
momentary axes. In the bears and giant panda
the congruence is less than in man, and it seems
impossible to determine even a "compromise" axis.
In procyonids the congruence is close and the
movement is a screw movement. Movement is
in general oblique: abduction coupled with ever-
sion and dorsal flexion of the foot, or adduction
coupled with inversion and plantar flexion (Sivers,
1931). X-ray photographs (fig. 79) show that
movement in this joint is relatively slight in Ailu-
ropoda and Ursus.
Transverse Tarsal Joint (Chopart's articulation)
A combination of rotatory and sliding joints,
between the head of the astragalus and the navic-
ular (rotatory) and the calcaneus and cuboid (glid-
ing). The axis of rotation runs longitudinally
through the head and neck of the astragalus and
the approximate center of the navicular; the cal-
caneus glides over the cuboid in an arc. Move-
ment, which involves compensatory adjustments
between the astragalus and calcaneus, is inversion
and eversion and /or abduction and adduction of
the foot. Dorsiflexion and plantar flexion of the
foot, which is the main movement of this joint in
man, is very slight. X-ray photographs (fig. 79)
show that in Ailuropoda and Ursus rotatory move-
ments in this joint are extensive, though less ex-
tensive than between the navicular and the distal
tarsal row.
Most students of the comparative anatomy of
the tarsus in quadrupeds (Tornier, 1888; Sivers,
1931; Schaeffer, 1947) have emphasized the trans-
verse tarsal and lower ankle joints, dismissing the
upper ankle joint as a simple hinge. In the tarsus
of the generalized carnivores the most conspicuous
difference is the relation of the axis of the upper
ankle joint to the remainder of the ankle and foot.
This difference is not apparent unless the astrag-
alus is examined in situ, with the foot lying flat
on the ground (fig. 78, A). Then the position of
the axis with relation to the surrounding structures
shows that the relation of the foot to the lower leg
differs significantly from species to species. Angles
142
FIELDIANA: ZOOLOGY :MEM0IRS, VOLUME 3
"'
^y ^
Y^
1
\^r
J^
y^
\j -'-
C^
PoboS
Ursus
Ailuropoda
Fig. 78. Dorsal (A) and anterior (B) views of right astragalus and calcaneus of Polos flavus (an arboreal forml and Ursus
arctos and Ailuropoda (terrestrial forms), to show differences in the angulation of the axis of the upper tarsal joint. In the
dorsal views the horizontal line is drawn at right angles to the long axis of the foot. The anterior views are drawn with
the foot flat on the ground, the horizontal line representing the horizon. The diagram associated with each drawing does
not show the normal position of the foot, but the indicated position of the foot if the tibia were oriented (A) with the trans-
verse axis of the inferior articular surface of the tibia parallel to the transverse axis of the body, and (B) with the long axis
of the tibia vertical. C, proximal articular surfaces of navicular and cuboid in the same positions as B.
were measured with a protractor on dried liga-
mentary preparations with the foot in normal un-
strained position. In dorsal view the axis is nearly
transverse to the long axis of the foot in Ursus and
Ailuropoda; actually it is rotated slightly counter-
clockwise ( 6 to 8), so that the foot would
have a slight tendency to toe out. In Claenodon,
a primitive Paleocene creodont, the axis is rotated
counterclockwise about 22. In Potos and other
procyonids, on the contrary, the axis is rotated
clockwise (22 in Potos, 15 in Procyon, 15 in Ailu-
rus), so that the foot would tend to toe in.
In anterior view (looking at the distal faces of
astragalus and calcaneus (fig. 78, B), there are
similar though less extreme differences. In Ursus .
and Ailuropoda the axis is tilted clockwise 15-20,
which would tend to produce moderate inversion
of the foot. This tilting is greater in procyonids
(50 in Potos) and would tend to produce strong
DAVIS: THE GIANT PANDA
143
Fig. 79. Tracings from X-ray photographs of the right foot of the panda Mei Lan, to show areas in which joint move-
ment takes place. A, medial view, foot abducted and inverted (solid line), superimposed on tracing of foot adducted and
everted (shaded) ; the tibia, fibula, and calcaneus were superimposed in tracing. In abduction-eversion the calcaneus is rotated
mesad on its long axis (note decreased width across sustentacular process trochlear process), in addition to sliding laterad
and proximad. Note, however, that the major movements of eversion-inversion and abduction-adduction take place in the
transverse tarsal joint and the more distal parts of the ankle. B, dorsal view, the foot adducted and inverted (solid line),
superimposed on tracing of foot abducted and everted (shaded). The calcaneus has rotated mesad on its long axis (note
position of sustentacular process and decreased width across sustentacular process trochlear process), in addition to sliding
laterad and proximad. Note that the major movements of eversion-inversion and abduction-adduction take place in the
transverse tarsal joint and the more distal parts of the ankle.
inversion of the foot. The angle is about 45 in
Claenodon.
Sivers pointed out that the lateral and medial
facets on the astragalus and calcaneus are more
convex (or concave) in Mustela and Gulo, and that
the facets are inclined toward one another. It
may be added that the articular surface of the
astragalar head is very extensive, and only part of
it contacts the concavity of the navicular at any
one time. This is likewise true of Procyon and
Potos. These conditions permit a considerable
range of inversion-eversion movement, wherein
the astragalus rotates in a screw movement on the
calcaneus, which remains relatively stationary with
respect to the cuboid (movement in the intertarsal
joint), while the astragalar head rotates extensively
in the concavity of the cuboid (movement in the
medial half of the transverse tarsal joint) . Exten-
sive inversion and eversion are obviously associ-
ated with the arboreal habits of these animals. It
is functional eversion that permits these animals
to apply the sole to a flat surface, as in standing
on the ground.
In Ursus and Ailuropoda, on the contrary, the
lateral and medial facets are flatter and are less
inclined toward one another, and the area of the
astragalar head exceeds the area of the concavity
of the navicular only slightly. This signifies a less
extensive range of movement (particularly of ever-
sion and inversion) in the ankle. Moreover, as
Sivers pointed out for Ursus, movement between
the astragalus and calcaneus (the lower ankle joint)
is largely horizontal rotation around a vertical
axis running through astragalus and calcaneus;
this is affirmed by our x-ray photos (fig. 79). This
would increase the stability of the ankle, and would
favor abduction and adduction rather than inver-
sion and eversion. It also explains the fact that
in the bears and panda the combined diameter
144
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
across the lateral and medial facets on the astrag-
alus exceeds the diameter of those on the calcaneus.
The following measurements of ranges of move-
ment were made on the fresh unskinned hind leg
(except Ailuropoda, which was skinned). The
Ursus americanus was about a quarter grown, the
other two fully adult. The tibia was placed in a
vise and the foot manipulated by hand by grasp-
ing the base of the metatarsals, the operator taking
care not to force the foot beyond its normal limits.
Angulation was read off directly on a protractor,
two or more readings being made for each position.
Prccjon
Abduction-adduction. . . . 32
Flexion-extension 130-135
Flexion (from right/ 0). -40--43''
Extension
(fromrightZO) -|-90--|-92
Eversion-inversion 87-89
Eversion 58-62
Inversion 27-29
iluropoda
Ursus
28-29
38
45
67-69
-1-45
-32
-1-90
-f35
48-50
42-50"
17
48-50
25
Differences in abduction-adduction are negligi-
ble among these three animals. Otherwise the total
range of movement is notably greater in Procyon
than in the bear or panda, and this presumably
reflects the arboi-eal habits of Procyon.
In Ailuropoda and Ursus not only is the range
of flexion-extension more restricted than in Pro-
cyon, but the pattern is different both from Procyon
and from each other (fig. 80). In Ursus flexion
and extension, measured from a line at right angles
to the tibial axis, are about equal. In Ailuropoda
the whole range of flexion-extension lies completely
outside the range in Ursus, and well below the 90
axis; i.e., the foot in Ailuropoda is permanently
extended on the tibia.
The situation is comparable, although less ex-
treme, for eversion-inversion (fig. 80). In Procyon
eversion exceeds inversion. The reverse is true of
Ursus, which also has a much more restricted
range of movement. In Ailuropoda the range of
movement is similar to that of Ursus, but is all
in the direction of inversion; the foot cannot be
everted on the tibia at all. I can find no differ-
ences in the transverse tarsal joint of these two
forms that would account for the differences in
eversion-inversion. The difference probably lies
in the torsion angle of the tibia (p. 115) and in-
clination of the upper ankle joint.
No detailed dissection of the tarsal ligaments of
Ailuropoda was made.
In summary, the ankle joint in the bears is a
relatively unspecialized structure, combining mod-
erate flexibility with adequate support (Davis,
1958) ; it is neither as flexible as the ankle of ar-
boreal forms, nor as stable as the ankle of cursorial
forms. The ankle joint of Ailuropoda, so far as
Eversion
Fig. 80. Diagrams of ranges of movement in the ankle joint of carnivores. A, eversion-inversion. B, flexion-extension. ^
(See figures in adjoining table). ji
DAVIS: THE GIANT PANDA
145
known, is very similar to that of the bears. Cei'-
tainly the resemblance is closer than in the hand
joint.
IV. REVIEW OF JOINTS
In the developing individual the primary gross
model of a joint is determined by intrinsic (heredi-
tary) factors, but the further shaping of the joint
depends almost wholly on extrinsic (non-heredi-
tary) mechanical factors (Muiray, 1936). The
importance of mechanical factors in determining
joint form is heavily underscored by the pseudar-
throses (joint-like structures in places where nor-
mally there should be no joint) that have been
described in the literature. Failure of a fracture
to heal may, even in the fully mature adult, lead
to the formation of a "a structure so exactly mim-
icking a normal joint that the first half of the word
'pseudarthrosis' does it less than justice" (Mur-
ray, 1936). Such pseudarthroses may involve
joint-like expansions of the apposed ends of the
bones, cartilage-covered articular surfaces, a cap-
sule, ligaments, and synovial fluid.
If only the gross model of an articulation is in-
herited, then natural selection can act directly only
on the gross model. The articulation is, of course,
a part of a total functional mechanism that is sub-
jected to selection. The articulation's response to
such extrinsic factors as posture and movement
may therefore, by limiting the range of possible
functional mechanisms, limit or channel the gene-
controlled changes in other elements of the total
mechanism and thus indirectly play an active role
in natural selection. In seeking a causal explana-
tion for the differences between two closely related
organisms, however, we must assign a passive role
to differences in the articulations. This will not
be true if we are comparing distantly related or-
ganisms (perhaps above the family level), where
differences in the gross model, attributable to in-
trinsic factors, are likely to be involved. Nor will
it be true for grossly adaptive differences, such as
those in the mandibular articulation of the panda,
if these involve differences in the gross model. The
chief value of the joints in comparisons between
closely related forms is, then, as extremely sensi-
tive indicators of differences in other elements
that are related mechanically to the joints.
Except for the mandibular joint, the joints of
Ailuropoda, so far as they have been studied, differ
little from those of Ursus. Such differences as
there are tend to increase the range of movement
in the joints. None of these differences seems to
depend on intrinsic factors other than the capacity
of the joint to respond to extrinsic factors.
THE MUSCULAR SYSTEM
The muscles of the Carnivora are comparatively
well known, but even for this order our knowledge
is at a primitive level. Descriptions are incom-
plete and inaccurate, often doing little more than
establish the fact that a given muscle is present in
species dissected. Even for the domestic carni-
vores the dog and the cat the standard reference
works are full of inaccuracies and are inadequately
illustrated. Most of the genera of Carnivora have
never been dissected at all.
Within an order as compact as the Carnivora
there are few differences of the "present" versus
"absent" variety (see Table 16, p. 197 1, and ques-
tions of muscle homology' are of no importance.
There has, however, been a good deal of adaptive
radiation within the Carnivora, as is obvious if
the agile predaceous cats are compared with the
lumbering semi-herbivorous bears, or the cursorial
cheetah with the burrowing badgers. Such dif-
ferences in habit are reflected in differences in the
muscular system. These muscular differences
their nature, their directions, their limitations
are important elements of the over-all problem
of evolutionarj- mechanisms. They show what
has happened (and what has not happened i to the
muscle pattern inherited by the Carnivora from
creodont ancestors. Such empirical data form the
basis on which the nature of mammalian evolution
at the sub-ordinal level must be judged.
How can such differences be detected and eval-
uated? Certainly not on the basis of existing
descriptions and illustrations.
DATA OF COMPARATIVE MYOLOGY
Observation indicates that within a gi-oup of
related organisms a muscle is responsive, within
limits, to mechanical demands in (li relative size,
and (2) position most favorable for the required
lever action. Limits are set, on the one hand, by
the heritage of the group; the cephalohumeral of
the Carnivora, for example, has never reverted to
the original deltoid and trapezial elements from
which it arose, no matter how mechanically ad-
vantageous such a course might be. On the other
hand, the structures surrounding a muscle defi-
nitely limit the range of adaptive change of a
muscle. No alteration can continue to a point
where it interferes with the vital activities of other
structures. A remarkable instance of this type of
limitation is seen in the temf>oral muscle of the
giant panda (see p. 69).
A few generalizations as to the mode of phylo-
genetic alterations of muscles at the sub-ordinal
level may be listed. These have been derived em-
pirically from direct observation.
1. The bony attachments of a muscle may wan-
der almost at random (within the limits of its area
of embryonic origin i, provided they do not en-
croach on some other vital structure. This is seen
throughout the muscular system. It is particu-
larly apparent, for example, in the origin of the
triceps in carnivores (fig. 81).
2. Phylogenetic decrease in the volume of a
muscle presents no problem, since surrounding
structures simply move in and occupy the vacated
space (e.g., loss of the short head of the biceps in
carnivores ) . The power of a given muscle is usu-
ally increased phylogenetically by increasing its
area of cross section (i.e., increasing the number
and or diameter of fibers i . In muscles with dif-
fuse origin this involves increasing the area of
origin, and this is accomplished in various ways:
(a) The bone surface may be increased, as in
the temporal fossa of the giant panda, or
the postscapular fossa on the scapula of
bears.
(b) Flat muscles may be reflected, like folding
a sheet of paper, to increase the total length
of origin without increasing the over-all
linear extent on the bone. This is seen in
the deep pectoral of the bears and giant
panda compared with those of more primi-
tive carnivores.
(c) Accessory origin may be gained from super-
ficial aponeuroses or from a tendon sheet
embedded in the muscle, as in the temporal
muscle of carnivores.
(d ) Surrounding muscles may be displaced from
their bony attachment, and arise or insert
instead on the fascia of other muscles. This
is seen in the deltoids of the giant panda.
3. It has long been known that muscles may
become more or less completely transformed into
I
146
DAVIS: THE GIANT PANDA
147
Canis
Felis
Ailuropoda
Fig. 81. Medial view of humerus of Cant's (after Bradley), Felis (after Reighard and Jennings), and Ailuropoda to show
variation in the origin of the medial head of the triceps.
tendons during phylogeny, and Haines (1932) has
demonstrated that tendons increase at the expense
of muscle substance during ontogeny in man. He
suggests that "tendon is lengthened by metamor-
phosis of muscle tissue in response to a limitation
of the range of possible contraction determined by
the nature of the attachment of the muscle."
Confirmation of this thesis is seen in the zygo-
maticomandibularis of the dog, where two layers
cross at an angle and the deeper layer is devoid of
muscle fibers exactly to the boundary of the more
superficial layer that partly overlies it. A similar
situation exists in the trapezius muscles of the
giant panda; muscle fibers are wanting exactly as
far as the border of the scapula (fig. 88). In both
of these examples pressure has limited the range
of contraction of part of a muscle, and in the areas
subjected to pressure, muscle tissue is replaced
by tendon.
Haines' further suggestion, that "it is no longer
necessary to postulate complex co-ordinating mech-
anisms to govern the sizes of the muscles, nor a
vast series of genes to suit muscles to their work,"
is an over-simplification. In cursorial mammals,
for example, the limb muscles are concentrated
near the center of limb rotation, resulting in long
terminal tendons. This is for the obvious mechan-
ical reason that such an arrangement reduces the
moment of inertia of the limb, not because of any
limitation of the range of possible contraction.
The tendons are already greatly lengthened in a
fetal horse.
Degree of tendinization may be (1) an active
mechanical adaptation, or (2) a reflection of limi-
tation of range of contraction resulting from (a)
pressure from surrounding tissues or (b) simple
degeneration, as in the short head of the biceps.
Tendinization of type (2) is probably an individ-
ual response to local conditions, not dependent
upon gene action.
4. The relation between muscle attachment and
bone relief at the site of attachment was reviewed
by Weidenreich (1922, 1926) and Dolgo-Saburoff
(1929, 1935). It is well known that the surface
relief of bone is attributable almost entirely to the
muscles and their adnexa, and the ligaments. The
nature of this relationship is not well understood.
Weidenreich emphasized that ridges and tuberosi-
ties represent portions of tendons or ligaments
that have ossified under tension and are then in-
corporated into the underlying bone. The extent of
this ossification tends to be directly proportional
to the mass of the musculature, and thus to the
force to which the connective tissue is subjected.
148
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Where a muscle mass is enlarged beyond the
available attachment surface on the bone, attach-
ment is extended onto the adjacent fascia; conse-
quently the size of a muscle cannot always be
judged from its mark on the bone (Weidenreich,
1922). Beautiful examples of this phenomenon
are seen in the limb musculature of Ailuropoda.
Transgression onto the fascia may lead to ossifi-
cation of the fascia and its incorporation into the
skeleton, as is easily seen in the development of
the sagittal crest in many mammals.
DATA OF MORPHOGENESIS
We know almost nothing of the genetic basis for
the differentiation and development of muscles,
of the relative roles of intrinsic (genetic) vs. ex-
trinsic (non-genetic ) factors, or of the parts played
by generalized and localized gene effects. The ex-
tensive catalog of genes in the laboratoiy mouse
compiled by Griineberg (1952) does not contain a
single reference to the muscular system. This al-
most total ignorance contrasts sharply with the
considerable body of such knowledge for the skele-
ton and joints, and makes it almost impossible to
postulate the nature of the machinery involved in
producing adaptive differences in the muscular
system.
The differentiation and growth of muscle in the
indi\-idual were reviewed by Scott (1957). There
is an intimate relation between differentiation and
gi-owth of a skeletal muscle and the neive supply-
ing it, and the nei-ve seems to be the determining
agent in this relationship. Initial differentiation
of muscle fibers and their gi-ouping into individual
muscles can take place in the absence of any ner\-e
connection; that is, muscles have a certain capac-
ity for self-differentiation. But without nen^e-
muscle connections the muscle fibers do not de-
velop beyond a certain stage and later undergo
degeneration. Yet Pogogeff and Mun-ay (1946)
and others have maintained adult mammalian
skeletal muscle in vitro for months, without inner-
vation of any kind, and during this time the tissue
regenerated and multiplied. The developing mus-
cles in the individual are at first independent of
the skeletal elements, to which they gain attach-
ment only later; a muscle develops normally even
in the absence of the skeletal elements to which it
normally gains attachment. Independence of the
musculature from a factor affecting the skeleton
was demonstrated in achondroplastic rabbits by
Crary and Sawin (1952), who found the muscles
of normal size whereas the bones with which they
are associated were shorter. The muscles had to
"readjust their bulk and area of attachment to the
new bone shapes." During early ontogeny, skele-
tal muscles grow by di\'ision of developing fibers
or by differentiation of additional muscle-forming
cells, but during later ontogeny, gi-owth is believed
to be exclusivelj' by hj'pertrophy of individual
fibers.
Growth of muscles in bulk, even in the adult,
seems to be controlled at least in part by the nerv-
ous system. In man, disease of peripheral nerves
(such as pohTieuritis) may be followed by abnor-
mal nei-\-e regeneration and associated h\-pertrophy
of the related muscles, and hypertrophy of the
masseters is often associated with evidence of dis-
order of the central nei-\'Ous system (Scott, 1957).
Such gi-owth is by hypertrophy of individual mus-
cle fibers.
Muscular hypertrophy as a hereditan,- condition
has appeared in various breeds of domestic cattle
(Kidwell et al., 1952). In this condition the mus-
cles are enlarged, and most authors (but not Kid-
well et al. ) describe duplication of muscles. The
effect is typically localized in the hind quarters
and loin (Kidwell et al. state that in their stock
the muscles of the withers and brisket were also
somewhat hypertrophied ) . All authors describe
the muscles as coarse-gi-ained, and mention a gen-
eral reduction in the quantity of fat, both sub-
cutaneous and intra-abdominal. Kidwell et al.
concluded from breeding exjjeriments that the con-
dition "appears to be inherited as an incomplete
recessive with variable expressivity." In other
words, a simple genetic mechanism capable of pro-
ducing a generalized effect on the musculature has
been demonstrated.
The data of Fuld (1901) reveal differences from
his control animals in the relative mass of certain
muscles of the hind limb in dogs that were bipedal
from puppyhood. Most of the limb muscles were
unaffected, but foiu* showed differences of more
than 5 per cent in their mass relative to the total
mass of hip and thigh muscles. These were the
gluteus medius (7.6 per cent heavier), quadriceps
extensor (6.4 per cent lighter), biceps femoris (8.2
per cent lighter), and adductors (9.4 per cent
heavier). Two of these differences (middle glu-
teal and biceps) are in the direction of the weight
relations found in man, whereas the other two are
in the opposite direction. The dogs were said to
hop rather than to walk on their hind legs, how-
ever, and the differences from the control animals
may well have been adaptive, or at least reflected
differences in the demands made on the muscles.
Under any circumstances they certainly were not
hereditary.
These scanty data provide few significant clues
to the nature of the morphogenetic machinery in-
volved in the evolution of adaptive differences in
the musculature.
DAVIS: THE GIANT PANDA
149
ABSOLUTE VS. RELATIVE
MUSCLE MECHANICS
Attempts to study muscle mechanics have dealt
almost wholly with absolute values absolute con-
tractile force per unit of muscle cross section, lever
actions of individual muscles or groups of muscles,
or direct measurements of the power of an organ,
such as a limb. This approach has yielded indif-
ferent results because of the complexity of even
the simplest bodily movement, and the still ob-
scure relation between nerve impulse and the in-
tensity of muscle reaction.
A. B. Howell attempted to determine the rela-
tions between various locomotor specializations
(cursorial, saltatorial, aquatic) and musculature by
comparing various representatives of such locomo-
tor types regardless of their taxonomic affinities.
This approach to muscle mechanics is indirect, and
involves no mechanical analysis or estimate of
forces. The intent is simply to discover a con-
sistent correlation between a particular function
and a particular modification of the muscle pat-
tern. It may be confidently assumed that any
such correlation is mechanically significant, even
though no engineering analysis is made. Howell
himself repeatedly expressed his disappointment
at the meager results of this method. It is appar-
ent that because of the diversity of genetic back-
ground in so heterogeneous an assemblage of more
or less remotely related forms, only the crassest
morphological convergences would be evident.
The lower the taxonomic level the more homo-
geneous the genetic background that lies behind
the muscle pattern. Among representatives of a
superfamily or family we may focus more sharply
on divergences from the basic muscle pattern of the
group, for differences at this taxonomic level are
not likely to represent the accumulated load of in-
numerable earlier specializations in different an-
cestral lines. Here any departure from the norm
may be assumed to be adaptive, even though the
mechanics are too complex or too subtle to ana-
lyze. For example, in a series of carnivores rang-
ing from most carnivorous to most herbivorous the
relative masses of the external masseter and zygo-
maticomandibularis vary reciprocally, whereas all
other elements of the masticatory musculature re-
main constant (Davis, 1955). Even without ana-
lyzing the complex and subtle functioning of the
masticatory complex we may be sure that in this
instance the mechanically significant alterations
are localized in these two muscles. Bringing rep-
resentatives of other orders, with their different
heritage, into this comparison would have ob-
scured this relation, which is valid only within the
masticatory pattern of the Carnivora. Besides mass
or area of cross section, the relative values of force
diagrams and leverage systems may be compared
among closely related forms in the same way.
Thus an insight into the functioning of a muscle
or a group of muscles may be had at second hand,
without the actual direct mechanical analysis, or
determination of absolute forces, that has so far
proved impossible to achieve.
The possibilities of this method of assessing rela-
tive muscle mechanics have not been explored. It
will be used here, so far as existing data permit.
NOMENCLATURE AND
ARRANGEMENT
The nomenclature used here is the BNA, with
such obvious modifications as are necessary be-
cause of differences from human anatomy.
There is, of course, no "proper" sequence in
which muscles can be arranged, and various sys-
stems have been advocated. The arrangement
adopted here is that of Howell's Anatomy of the
Wood Rat, which is largely topographical. It may
be suggested that the index is a more satisfactory
means of locating a given description than at-
tempting to find it via some system of arrangement.
Innervation of muscles is given only in special
cases, since the nerve supply of carnivore muscles
is given in any standard anatomy of the dog or cat.
Perhaps the most important consideration in
evaluating muscle (and skeletal) differences within
an order or family is an accurate picture of the
bony attachments. This cannot be obtained from
verbal descriptions alone; only carefully drawn
maps will do. The exact areas of attachment of
all muscles (except axial and a few others) in
Ailuropoda have therefore been carefully plotted
on the bones, and appear in the section on the
skeleton. Unfortunately, comparable data for
other carnivores exist only for the dog (later edi-
tions of Bradley) and cat (Reighard and Jennings).
I. MUSCLES OF THE HEAD
A. Superficial Facial Musculature
M. platysma is much reduced. It extends as a
band of rather uniform width from a point above
and behind the auditory meatus to the corner of
the mouth. A few of the dorsal fibers swing up-
ward in front of the ear, to lose themselves in the
superficial fascia. Anteriorly a few of the most
dorsal fibers are separated from the main mass,
arising over the zygoma.
M. buccinator (figs. 82, 84) is a heavy flat
muscle sheet that forms the foundation of the
cheek. It is not divisible into buccal and molar
150
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
parts as it is in most mammals. Instead, the
muscle forms a uniform sheet of fibers that con-
verges partly into the mucosa of the lips near the
angle of the mouth, and partly into a horizontal
raphe running back from the angle of the mouth.
The dorsal fibers arise from the alveolar surface
of the maxilla just outside the last upper molar,
beginning at about the level of the middle of this
tooth. The line of origin runs caudad onto the
rugose triangular area immediately behind the
tooth. Ventrad of this area, fibers arise from the
pterygomandibular ligament, which extends cau-
dad across the inner face of the internal pterygoid
muscle. The ventral fibers arise from the alveolar
surface of the mandible, just outside the molar
teeth, beginning behind the last lower molar and
extending as far forward as the middle of the first
lower molar.
The remaining superficial facial muscles were
damaged in removing the skin and were not dis-
sected.
B. Muscles of the Ear
M. levator auris longus (cervico-auricularis-
occipitalis of Huber) is a fan-shaped sheet arising
from the dorsal midline just behind the posterior
end of the sagittal crest. There is no division into
two parts. The posterior half of the muscle in-
serts on the pinna. The anterior half is continued
forward over the top of the head.
M. auriculus superior is a narrow band lying
behind, and partly covered by, the levator auris
longus. Arising from the midline beneath the
levator auris longus, it inserts on the pinna just
caudad of that muscle, and separated from it by
the insertion of the abductor auris longus.
M. abductor auris longus lies immediately
anterior to, and partly above, the auriculus supe-
rior, and has approximately the same width. Dis-
tally it emerges from beneath the levator auris
longus, and inserts on the pinna just behind it.
M. auriculus inferior lies wholly beneath the
levator auris longus, and has the same general re-
lations. It is more powerfully developed than the
auriculus superior or the abductor auris longus,
and is more than twice as wide.
M. abductor auris brevis is the most caudal
of the auricular muscles. Its origin is beneath
that of the levator auris longus, but the belly of
the muscle emerges and inserts low on the posterior
face of the pinna.
M. adductor auris superior (auricularis ante-
rior inferior of Huber) is a narrow band arising
from the posterior end of the scutiform cartilage.
It inserts on the anteromesal face of the pinna.
M. adductor aris medius arises from the ex-
treme posterior end of the scutiform cartilage, be-
neath the origin of the superior. It extends as a
narrow band back to the posterior surface of the
pinna, where it inserts proximad of the abductors.
C. Masticatory Musculature
The masticatory muscles, which are chiefly re-
sponsible for the characteristic skull form of
Ailuropoda, are remarkable for their enormous
development. Otherwise they do not differ much
from the typical carnivore pattern. In all Carni-
vora the temporal is the dominant element of the
masticatory complex, forming at least half of the
total mass of the masticatory muscles. The in-
sertion tendon of the temporal extends into the
substance of the muscle as a tendinous plate, into
which most of the muscle fibers insert. Thus the
temporal is a bipennate (or if several such tendi-
nous plates are present, a multipennate) muscle,
in which the functional cross section per unit of
volume is much greater than in a parallel muscle
such as the masseter (Pfuhl, 1936). In carnivores,
because of the form of the mandibular articulation,
fast snapping movements of the jaws depend
largely on the masseter, whereas slower and more
powerful cutting and crushing movements depend
largely on the temporal.
The masticatory muscles arise ontogenetically
from the mandibular arch, by condensation about
the peripheral end of the mandibular nerve. Other
muscles arising from the mandibular arch, and
likewise supplied by the third branch of the tri-
geminal nerve, are the anterior belly of the digas-
tric, mylohyoid, tensor tympani, and tensor veil
palatini.
M. temporalis (figs. 82, 83) is enormously de-
veloped, filling the greatly expanded temporal fossa
except for a small area behind the orbit that is
occupied by fat. In an old, badly emaciated male
(Mei Lan) this muscle weighed more than twice
as much as in a black bear of comparable size, and
the temporal and zygomaticomandibularis together
nearly three times as much. The muscle is cov-
ered externally by a tough deep temporal fascia,
more than half a millimeter thick, that arises from
the sagittal and lambdoidal crests and postorbital
ligament and extends to the superior border of the
zygomatic arch. A few superficial fibers of the
temporal muscle attach to the zygomatic arch im-
mediately behind the temporal fascia and insert
into its inferior edge, thus forming a tensor of the
temporal fascia.
The external face of the temporal muscle is cov-
ered with an extremely heavy tendinous aponeu-
rosis, the deep temporal fascia, from which the j
DAVIS: THE GIANT PANDA
Planum tendineum temporalis
151
Lig. postorbitale
M. temporalis
M. buccinator; p. buccalis (sup.)'
M. buccinator; p. buccalis (inf.)
Raphe tendinosa
Fig. 82. Masticatory muscles of Ailuropoda, seen from the left side. The temporal and masseteric fasciae have been re-
moved, and a window cut in the temporal muscle to expose the tendinous plane that separates the superficial and deep
layers of the temporal muscle. The superficial and deep layers of the masseter are inseparable anteriorly. Note that the in-
sertion of the superficial masseter does not extend posteriorly onto the angular process of the mandible.
superficial fibers of the muscle take origin. As is
usual in carnivores, the muscle is divided into
superficial and deep parts, separated by a heavy
tendinous plate, the insertion tendon of the mus-
cle, that extends between the sagittal crest and
the superior and posterior borders of the coronoid
process. Muscle fibers attach to both surfaces of
this tendinous plate. Additional tendon sheets
embedded in the substance of the muscle insert
into the coronoid process (fig. 83), making this
complex a truly multipennate muscle composed
of innumerable short fibers. These additional ten-
don sheets do not occur in Ursus (Sicher, 1944,
fig. 13; Schumacher, 1961a), and the temporal is
therefore a simpler and less powerful muscle in
the bear.
The superficial part arises from the whole deep
surface of the tendinous aponeurosis except for a
small area near the orbit, and, at the periphery of
the muscle, from the edges of the temporal fossa.
The fibers converge to insert on the external face
of the coronoid process of the mandible and into
the external surface of the tendinous plate. Along
its inferior border this muscle is incompletely sep-
arable from the zygomaticomandibularis.
The deep part of the temporal is much thicker
than the superficial part and its structure is more
complex. A tendinous sheet extends between the
prominent crest running obliquely upward on the
floor of the temporal fossa, some distance above
the superior orbital crest, and a crest on the coro-
noid process above the mandibular foramen. This
sheet separates the anterior part of the deep tem-
poral into superficial and deep parts. Additional
smaller tendon sheets, embedded in the substance
of the muscle, eventually attach to the inner face
152
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
M. temporalis
Aponeurosis temporalis
Fascia temporalis post
ArcUS ryfjninnJirilft / 1
M. zygomaticomandibularis
M. massctericus prof.
M. massetericus superf L
Canalis mandibularis
Sinus I
Tendo M. temporalis
Fossa olfactoria
Crista orbitalis sup.
Foramen opticum
Crista orbitalis inf.
Pars nasalis pharyngis
A. maxiltaris int.
Tendo accessorius M. temporalis
M. pter\'goideus int.
Gl. sublijigualis
M. genioglossus
M. mylohyoideus
V.Jacialis ex I.
M. digastricus
Proc. angularis mandib.
Fig. 83. Frontal section through head of an old emaciated male Ailuropoda (Mei Lan). The section passes through the
coronoid process of the mandible (see inset).
of the coronoid process. Muscle fibers arise from
tiie whole floor of the temporal fossa, and from the
deep surfaces of the several tendon sheets. Some
of the fibers insert into the surface of the coronoid
process, the insertion area extending ventrad as
far as the mandibular foramen. Other fibers in-
sert into the superficial surfaces of the several ten-
don sheets.
The temporal is an elevator of the mandible.
Because of its multipennate structure it produces
slow but very powerful movements.
M. zygomaticomandibularis (fig. 83) is rela-
tively larger than in any other carnivore examined.
It is completely hidden beneath the masseter and
zygomatic arch, and fills the masseteric fossa.
Origin is from the whole internal face of the zygo-
matic arch. The fibers converge toward the mas-
seteric fossa, into which they insert by both muscle
and tendon fibers. Tendon sheets embedded in
the muscle near its insertion attach to crests on
the floor of the masseteric fossa, and these tendons
increase the available insertion area. The flber
direction of the zygomaticomandibularis is down-
ward, mesad, and slightly backward. In the sag-
ittal plane the fibers are almost vertical, forming
an angle of about 80 with the occlusal plane. In
the frontal plane the angle is about 75 with the
transverse axis of the head. In both planes the
angles become increasingly vertical as the jaw is
opened.
The zygomaticomandibularis is primarily an
elevator of the mandible. The muscle of one side
of the head, in conjunction with the pterygoids of
the opposite side, shifts the mandible transversely
toward the side of the contracting zygomatico-
mandibularis. This motion is the grinding com-
DAVIS: THE GIANT PANDA
153
ponent of the jaw movements in Ailuropoda and
other carnivores.
M. masseter (figs. 82, 83) is powerfully devel-
oped. It is more or less divisible into the usual
two layers, although these are fused and insep-
arable anteriorly.
The pars superficialis is a thin sheet covering
all but the posterior part of the profunda. More
than the proximal half of the external face of the
superficialis is covered with a heavy tendinous
aponeurosis (aponeurosis 1 of Schumacher, 1961a),
which is continuous posteriorly with the aponeu-
rosis of the profunda. The muscle arises by this
aponeurosis and by underlying muscle fibers from
the anterior half of the inferior border of the zygo-
matic arch. The fibers run backward and down-
ward at an angle of about 45 with the occlusal
plane, to insert non-tendinously into the inferior
edge of the mandible, immediately below the coro-
noid fossa, the insertion extending back as far as
the angular process. At its insertion the muscle
forms a tendinous intersection with the internal
pterygoid . The posteriormost fibers do not extend
beyond the angular process at the posterior end of
the mandible to insert into the stylomandibular
ligament, as they do in Ursus and other carnivores.
The internal face of the superficialis is in veiy
intimate contact with the underlying profunda,
the two layers being inseparable anteriorly.
The pars profunda is covered by the superfcialis,
except for a narrow area along its posterior edge.
It arises by fleshy and tendon fibers from the en-
tire inferior border of the zygomatic arch, back to
within 10 mm. of the mandibular fossa. The fibers
have a slightly more vertical direction than do
those of the superficialis. A tendon sheet em-
bedded in the posterior part of the profunda,
attaching to the zygomatic arch, partly divides
the muscle into superficial and deep layers. The
external face of the mandibular half of the pro-
funda is covered with a heavy glistening aponeu-
rosis (aponeurosis 2 of Schumacher, 1961a). In-
sertion is made by means of this aponeurosis into
the mandible along the inferior border of the coro-
noid fossa. The fibers run backward and down-
ward at an angle of about 55 with the occlusal
plane.
The masseter is an elevator of the mandible.
Because it is composed of long parallel fibers it
produces quick snapping movements, relatively
less powerful than those of the temporal muscle.
M. pterygoideus internus (figs. 70, 83, 84;
lateralis of authors) is a rectangular group of par-
allel fibers arising from the ventral edge and outer
side of the perpendicular plate of the palatine,
pterygoid, and sphenoid bones. The muscle is
thin and delicate posteriorly, and is relatively
smaller than in any other known carnivore. It
shows a tendency to break up into three or more
subequal elements. Insertion is into the promi-
nent fossa on the inner side of the lower border
of the ramus of the mandible, extending onto the
angular process. A few of the delicate posterior
fibers insert into the anterior end of the stylo-
mandibular ligament.
The internal pterygoids acting together elevate
the mandible. Unilateral contraction simultane-
ously elevates the mandible and shifts it toward
the contralateral side.
M. pterygoideus externus (figs. 83, 84; medi-
alis of authors) is much shorter, but considerably
thicker, than the internal pterygoid muscle. Its
lateral end lies dorsad of the internal pterygoid,
and its medial end posterior to it. Origin is by
two heads, which are separated by the buccinator
nerve. The more ventral head arises from the
outer side of the pterygoid plate at its posterior
end, extending as far back as the combined fora-
mina ovale and rotundum. The other head con-
tinues this origin up onto the skull, behind the
optic foramen. The two heads fuse, and the re-
sulting muscle extends straight laterad to its in-
sertion, which is into the prominent pit on the
anteromedial end of the condyle of the mandible.
The two external pterygoids are antagonistic.
Unilateral contraction shifts the mandible toward
the contralateral side.
Discussion of Masticatory Muscles
We have seen (p. 72) that the skull in Ailuro-
poda, and in herbivorous carnivores in general, is
designed to promote the production of maximum
forces at the level of the cheek teeth by (a) im-
proving lever advantages, (b) increasing the space
available to muscle tissue, and (c) resisting dis-
integrating forces.
The active forces themselves are of course sup-
plied by the craniomandibular muscles. These
may further enhance the efficiency of the mastica-
tory apparatus in three purely morphological ways:
(a) generalized increase in mass of contractile tis-
sue, (b) selective increase in mass, involving only
those elements that produce the forces involved in
pressure and grinding movements, and (c) increase
in functional' cross section. Each of these is evi-
dent in the masticatory musculature of the giant
panda.
1 The functional cross section is a section at right angles
to the fibers. The anatomical cross section is a section at
right angles to the long axis of the muscle. In a parallel-
fibered muscle these two sections may coincide; in a pennate
muscle they never do.
154
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Lif. ptervgomandib. {cut & reflected)
M. ptcrygoideus int.
M. pterygoideus ext.
"Hamulus pterygoideue
Capsula orttcuijris
Lig. stylomandib. (cut)
Proe. angukais
M. mylohyoideus
Fig. 84. Masticatory muscles of Ailuropoda, medial view.
Generalized Increase in Mass. I have used
brain weight as a standard for computing an index
of the relative mass of the total masticatory mus-
culature of one side of the head. The data are
given in the accompanying Table 12. The weights
are all from zoo animals, and consequently the
values for the musculature are undoubtedly low,
although all except the panda were in good flesh
at time of death. The panda (Mei Lan), in addi-
tion to his years in captivity, was much emaciated
at the time of his death. Nevertheless these fig-
ures show that the relative mass of the masticatory
musculature in Ailuropoda is at least twice as great
as in bears of comparable body size.
That this increase is truly generalized is shown
by the fact that the mass of the digastric, a muscle
not involved in jaw closure, equaled 30 per cent
of brain weight in Ailuropoda, whereas in the bears
it was less than 10 per cent of brain weight. It is
impossible to determine whether both bellies of
the digastric are equally hypertrophied; certainly
the anterior belly is involved.
The masticatory musculature, except for the
posterior belly of the digastric, is derived from the
mandibular arch of the embryo. Also derived
from this arch are the mylohyoid, tensor tympani,
and tensor veli palatini. The mylohyoid is in no
way involved in jaw closure, yet in Ailuropoda it
is hypertrophied like the craniomandibular mus-
cles (p. 157). I was unable to decide from inspec-
tion whether the tiny tensors were relatively larger
than in the bears. It is evident, however, that
what is enlarged in the panda is not a functional
unit, but a morphological unit the muscular de-
rivatives of the mandibular arch. The fact that all
are hypertrophied shows that, in this instance at
least, the morphological unit is also a genetic unit.
Indeed, hypertrophy extends in a decreasing gra-
dient, beyond the derivatives of the mandibular
arch, to the entire musculature of the anterior
part of the body (p. 182). The morphogenetic
mechanism involved in the hypertrophy is prob-
ably very simple. Selection undoubtedly favored
an increase in the mass of the jaw-closing muscles
Table 12. RELATIVE MASS OF MASTICATORY MUSCULATURE
Masticatory
Musculature Digastric
(gms.) (gms.)
Ailuropoda melanoleuca ( d" ad.) 890 92
Ursus americanus ( 9 ad.) 322 26
Thalaretos marilimns ( cf ad.) 910 86
Mean of two brain weights (489 gms., 507 gms.) given by Crile and Quiring (1940). The brain of the polar bear from
which I dissected the muscles was not weighed.
Brain
Index:
Masticatory
Musculature
(gms.)
Brain
277
3.2
238
1.4
498*
1.8
I
DAVIS: THE GIANT PANDA 155
in the panda, but the results extend far beyond other mammals, including man) the insertion ten-
the functional unit. don of the temporal muscle continues into the
Selective Increase ln Mass. Relative masses muscle substance as a broad tendon sheet. Fibers
of individual components of the masticatory com- of the temporal muscle insert obliquely into both
plex may be compared by reducing each to a sides of this tendon sheet, and the temporal is
percentage of the mass of the total masticatory therefore a pennate muscle. In Ailuropoda the
complex (Davis, 1955). Data are given in the temporal has been converted into a multipennate
accompanying table. muscle by tendinization of numerous fascial planes
Table 13. RELATIVE WEIGHTS OF MASTICATORY MUSCLES IN CARNIVORES
(Including data from Davis, 1955)
Ailuropoda Tremarctos Ursus Procyon Thalarctos Canis Felis
[Mei Lan| ornatus americanus* lotor maritimus familiaris onca
Wt.ingms. % % % % % % %
Masseter superf 44 5 7.5 10 5 1 f 15 21
12
Masseter prof 60 7 2.5 2 3 J [ 3 2.5
Zygomaticomand 188 21 14 11 13 7 6 2.5
Temporalis 477 54 58 62 63 66 58 59
Pterygoideus internus 18 2 7 5 6 4 7.5 6.5
Pterygoideus externus 11 1 1 1 1 1 0.5 0.5
Digastric 92 10 10 9 9 10 9.5 8
Totals 890 100 100 100 100 100 99.5 100
Means of two specimens; data for one individual from Starck (1935). All other figures from one individual each.
I have pointed out elsewhere (Davis, 1955) that
in the Carnivora the masses of only two muscles,
the superficial masseter and the zygomaticoman-
dibularis, appear to vary significantly with differ-
ences in food habits, and that these two muscles
vary reciprocally. A large superficial masseter
appeared to be associated with carnivorous habits,
a large zygomaticomandibularis with herbivorous
habits. The additional data presented here con-
firm this relation. Moreover, in Ailuropoda the
superficial masseter is relatively smaller (except
in Procyon, where it is equally small) and the
zygomaticomandibularis larger, than in any other
carnivore examined.
The masseter, because it is composed of long
parallel fibers, is particularly effective in producing
quick snapping movements of the mandible a
movement obviously important to predaceous car-
nivores. There is an important horizontal compo-
nent in the action of the zygomaticomandibularis.
This muscle, which in bulk far exceeds the more
horizontally situated but tiny external pterygoid,
is primarily responsible for lateral shifting of the
mandible a movement important to herbivorous
carnivores. Thus, in addition to the generalized
increase, there is a selective increase in mass among
the masticatory muscles, and the results conform
to the requirements of differing dietary habits.
Increase in Functional Cross Section. In
the temporal muscle of all carnivores (and of many
in the substance of the muscle, with muscle fibers
attaching to both surfaces of these tendon sheets.
What are the mechanical advantages of penna-
tion in a muscle? A pennate fiber is the diagonal
of a parallelogram of which one component repre-
sents force along the axis of the insertion tendon
while the other component tends to pull the inser-
tion tendon toward the origin. Only the first of
these two components represents useful work. The
second is waste effort, whose magnitude varies
with the angle of pennation but in all cases repre-
sents an important fraction of the total energy of
the contracting fiber. There is no such waste of
energy in a parallel-fibered muscle, which is there-
fore more efficient than a pennate muscle. Some
advantage must offset the inefficiency of the pen-
nate structure.
Eisler (1912) suggested maximum utilization of
attachment area as a factor in the pennation
of muscles. He pointed out that powerful mus-
cles are pennate in situations where available at-
tachment area is limited, whereas other powerful
muscles remain parallel-fibered in situations where
the attachment area can be expanded. Eisler com-
pared the multipennate human deltoid, with its
anatomically restricted areas of attachment, with
the parallel-fibered gluteus maximus, which has
been able to expand its areas of attachment un-
hindered. Available attachment area is obviously
a limiting factor in the temporalis of Ailuropoda.
156
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
The temporal fossa has been expanded in all direc-
tions, apparently to the limits that are compatible
with other vital functions of the head (p. 46). The
mass of the muscle, particularly its area of origin,
cannot be increased further to achieve additional
power.
Pfuhl (1936) attempted to work out the mechan-
ics of pennate muscles. The work (a) of a muscle
is expressed in two terms: force (F), and the dis-
tance (rf) through which the force is exerted :
a=F .d
(1)
The force of a muscle may be expressed by the
equation
F = k . q (2)
where q is the functional cross section and A; is a
constant representing the unit of muscle power.'
Thus for any value of a in equation (1) the propor-
tion oiF can be increased by increasing the func-
tional cross section of the muscle, that of d by
increasing its length. For a given mass of muscle
tissue, maximum force would therefore be achieved
by arranging the muscle as a series of minimally
short parallel fibers, which would give maximum
functional cross section. Such an arrangement
would usually produce architectural difficulties,
since areas of origin and insertion would become
unduly large. An alternative is the arrangement
of the fibers in pennate fashion between more or
less parallel sheets of bone or tendon. This loses
a portion of the total energy of the muscle, as
shown above, but enormously increases the func-
tional cross section and therefore the power per
unit of mass. Thus pennation is a device permit-
ting maximum production of force in a minimum
of space, and utilizing limited attachment area on
the skeleton. This effect is multiplied by multi-
pennation.
The craniomandibular musculature of Ailuro-
poda represents an extension of conditions in the
bears, which in turn are a modification of condi-
tions in more generalized carnivores. Indeed, in
Tremarctos, the most herbivorous of the bears, the
craniomandibular musculature appears to be about
intermediate between Ursus and Ailuropoda.
As will appear in the sequel, the generalized in-
crease in the mass of the craniomandibular mus-
cles of Ailuropoda is associated with a generalized
hypertrophy of the skeletal muscles of the shoulder
region, and probably has a very simple genetic
basis. The morphogenetic basis underlying the
other two adaptive modifications increase in rela-
' The unit of muscle power is the tension produced by a
muscle with a functional cross section of 1 cm'. For pur-
poses of calculation it is assumed to be 10 kg.
tive mass of individual muscles, and increase in
functional cross section is unknown.
D. Interramal Musculature
These three muscles form a topographic, but not
a morphological, unit. Ontogenetically they are
derived from two different sources: the anterior
belly of the digastric and the mylohyoid (from the
mandibular arch) are supplied by the trigeminal
nerve; the posterior belly of the digastric and the
stylohyoid (from the hyoid arch) are supplied by
the facial nerve. At least the elements derived
from the mandibular arch are hypertrophied like
the craniomandibular muscles derived from this
arch. Of the elements derived from the hyoid arch,
the stylohyoid is absent in Ailuropoda and there
is no way of determining whether hypertrophy of
the digastric involves the fibers of its posterior belly.
M. digastricus (figs. 82, 83, 85) is a powerfully
developed muscle, triangular in cross section, with
the base of the triangle ventrad. The muscle has
a thickness of 22 mm. The mass of the muscle is
shot through with powerful longitudinal tendon
fibers. Origin is from the paroccipital process and
the ridge connecting this process with the mastoid
process. The muscle is covered with a tendinous
aponeurosis at its origin; there is also a small ac-
cessory tendinous origin from the mastoid process.
Insertion is into the inner surface of the mandible,
from a point opposite the second molar tooth back
as far as the mandibular foramen.
A fine tendinous inscription runs across the belly
of the muscle near its middle, marking the juncture
of the anterior and posterior bellies.
The digastric is relatively much larger than in
the bears (Table 12) , but there is no way of deter-
mining whether both bellies share in this hyper-
trophy. Certainly the anterior belly is enlarged.
M. stylohyoideus is absent. This muscle is
tjT)ically composed of two parts in carnivores, a
superficial slip external to the digastric and a
deeper part internal to the digastric. Either may
be absent, although there seems to be no previous
record of both being absent simultaneously. Noth-
ing corresponding to either part could be found in
the specimens of Ailuropoda dissected.
M. mylohyoideus (figs. 83, 84, 85) is a thick
sheet that fills, with its fellow, most of the space
between the rami of the mandible. Anteriorly a
small space exposes the end of the genioglossus.
The muscle arises from the medial surface of the
mandible just below the alveoli of the teeth, from
a point opposite the first molar to the angular
process. The general direction of the fibers is
transverse, although anteriorly and posteriorly
DAVIS: THE GIANT PANDA
157
M. geniogloesu*'
M. mylohyoideus'
/ M' geniogloasus
M geniohyoideus
litifualis
M. styloglossus
M. pterygoid
eus int.
M. pterygoid
eus ext.
M. thyreopharyngeua: constr. phar. post
M. stemothyreoideus
oc. mastoideus
stylohyale
Proe. paroceipitalis
N. hypogU>ssus
M. constrictor pharyngis medius
M. hyogloosus
M. thyreohyoideus
M. cricothyreoideus pars recta
M. cricothyreoideus pars obliqua
Fig. 85. Muscles of the head of Ailuropoda, ventral view.
they diverge to the mandibular symphysis and the
hyoid, respectively. Insertion is made in the usual
way into a median raphe with the opposite muscle,
and posteriorly into the hyoid bone. Medially the
inner surface of the mylohyoid is almost insepa-
rably united to the geniohyoid.
The mylohyoid is much thicker, particularly
near its origin (fig. 83), than is the mylohyoid of
bears.
E. Muscles of the Tongue
The extrinsic muscles of the tongue show none
of the hypertrophy that characterizes the cranio-
mandibular muscles. Ontogenetically these tongue
muscles arise from the ventral portion of the occip-
ital myotomes. They are innervated by the hypo-
glossal nerve.
M. styloglossus (fig. 85) takes extensive origin
from the stylohyal segment of the hyoid appara-
158
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
tus. The fibers diverge over the ventrolateral sur-
face of the tongue before they disappear into the
substance of the tongue itself.
M. hyoglossus ifig. 85) arises from the inferior
surface of the body of the hyoid, except for the
area occupied medially by the origin of the genio-
hyoideus, and the proximal part of the posterior
horn. The fibers run straight anteriorly for a short
distance before they penetrate the tongue, behind
and laterad of the genioglossus and mesad of the
styloglossus.
M. genioglossus (figs. 83, 85) is a narrow band
arising from the sjTnphysis just laterad of the mid-
line. The origin of this muscle is ventral and lat-
eral to the origin of the geniohyoideus. The
muscle runs posteriorly, separated from the ven-
tral midline by the geniohyoideus, and enters the
tongue partly anterior to and partly medial to the
hyoglossus.
IL MUSCLES OF THE BODY
A. Muscles of the Neck
1. Superficial Group
M. sternomastoideus (fig. 86) is a heavy flat
band about 40 mm. wide at its widest part (near
its insertion). It arises, partly tendinously and
partly fleshily, from the anterior border of the
manubrium and the proximal end of the first
costal cartilage. The muscle widens somewhat at
its insertion, which is made on the lateral and ven-
tral borders of the mastoid process. There is no
indication that the sternomastoideus fuses with its
mate at the midline.
M. cleidomastoideus (fig. 86) arises from the
dorsal edge of the stemomastoid, at a point about
70 mm. anterior to the origin of the latter muscle.
With a maximum width of only 25 mm., it is con-
siderably narrower than the sternomastoideus.
The two muscles run forward side by side, the
cleidomastoideus inserting on the lower part of the
lambdoidal crest as a direct continuation of the in-
sertion of the sternomastoideus, although the two
muscles remain completely separate.
2. Supra- and Infrahyoid Group
M. omohyoideus (figs. 86, 89) is a narrow rib-
bon, about 16 mm. wide, arising from the coraco-
vertebral angle of the scapula. It runs forward
and downward, passing between the scalenus and
the stemohyoideus. Near its insertion it divides
into two bellies. The larger of these inserts on the
hyoid, deep to the insertion of the stemohyoideus.
The other belly inserts aponeurotically on the ven-
tral face of the digastric, near its medial border.
M. stemohyoideus figs. 86, 87, 89, 90) arises
from the anterodorsal surface of the manubrium,
a few of the most lateral fibers reaching the costal
cartilages. It runs craniad as a narrow, flat band,
in contact with its mate of the opposite side near
its origin, but diverging from it farther anteriorly.
Insertion is made on the thyrohj-al element of the
hyoid.
M. stemothyroideus (figs. 85, 87, 89, 90) is
inseparable from the sternohyoid at its origin and
as far forward as a tendinous intersection which
crosses the common mass of these two muscles
about 40 mm. in front of the manubrium. Ante-
rior to this p>oint the sternothyroid lies partly
above (dorsal ) and partly lateral to the sternohyoid.
It inserts on the thyroid cartilage, just above the
insertion of the sternohyoid.
M. thyrohyoideus (figs. 85, 87, 89) is a wide,
flat band on the ventrolateral surface of the thy-
roid cartilage. Arising from the posterior border
of the thyroid cartilage, just laterad of the mid-
line, the fibers nm anteriorly to their insertion on
the posterior border of the thyrohyal and the body
of the hyoid.
M. geniohyoideus (fig. 85) is a narrow band
running from the symphysis mandibuli to the body
of the hyoid, closely applied to its fellow of the
opi>osite side. Arising from the s>"mphysis deep
to and laterad of the genioglossus, it inserts on the
anteroventral surface of the body of the hyoid,
just laterad of the midline.
3. Deep Lateral and Subvertebral Group
M. scalenus (figs. 86, 89) is divisible into the
usual longus and breris. The short division Ues
mostly beneath the much more powerful long divi-
sion. The scalenus longus arises by short, stout
tendons from the third to seventh ribs, its origins
interdigitating with the sraratus anticus. The
longus is subdivided into a dorsal part, which arises
from the second to the fifth ribs, and a medial part
from the sixth and seventh ribs. The bre\Ts arises
fleshily from the first rib near its junction with the
costal cartilage. The two divisions unite in the
cervical region, and the resulting common mass j
inserts on the transverse processes of the last five
cervical vertebrae.
M. longus colli arises from the ventral surfaces
of the bodies of the first six thoracic vertebrae and
from the ventral sides of the transverse processes
of the sixth to third cervical vertebrae. The usual
simple distinction of the thoracic and cervical parts
of the muscle because of difference in their fiber
directions is scarcely possible on the present speci-
men. The fibers arising from the thoracic verte-
brae are gathered into a tendinous band that in-
a
3
2
I
>>
o
Xi
o
t
3
2
s
o
^
3
.
E
oo
!2
a
U)
c
C^
o
T3
J
159
160
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
serts into the transverse process of the sixth cer-
vical. The fibers from the cervical vertebrae have
the customary insertion into the next vertebra
craniad of the one from which they arise, and into
the ventral surface of the arch of the atlas.
M. longus capitis is a prominent subcylindri-
cal muscle, somewhat flattened dorsoventrally. It
arises by fleshy fasciculi from the tips of the trans-
verse processes of the sixth to the second cervical
vertebrae. Insertion is into the prominent scar
on the ventral side of the basioccipital.
M. rectus capitis ventralis is a very slender
muscle lying mesad of the longus capitis, and in
contact with its mate of the opposite side at the
midline. It has the customary origin from the
ventral surface of the body of the atlas, and in-
sertion into the basioccipital mesad and caudad
of the longus capitis.
B. Muscles of the Trunk
1. Muscles of the Thorax
M. panniculus carnosus is rather feebly de-
veloped; the dorsal division is represented only by
an almost insignificant vestige. The borders of
the ventral division do not reach the midline either
dorsally or ventrally. A few fibers arise on the
inner surface of the thigh, and the sheet then
broadens as it passes anteriorly, reaching its great-
est width over the posterior ribs. At this point it
is approximately 170 mm. from the dorsal midline
and 80 mm. from the ventral. The sheet then
gradually decreases in width as it passes craniad.
At the point where it passes under the pectoralis
it is only about 50 mm. wide. The ventral fibers
insert on the bicipital arch, the dorsal ones on the
inner face of the pectoralis profundus.
The dorsal division is represented only by two
narrow ribbons, lying immediately dorsad of the
ventral division, that run up onto the shoulder for
about 50 mm. and insert into the epitrochlearis
immediately below the latissimus.
M. pectoralis superficialis (fig. 89). As in the
bears, the superficial pectoral sheet is a compound
muscle composed of the pectoralis superficialis an-
teriorly and the reflected posterior edge of the pro-
fundus posteriorly. Fusion is so intimate that the
boundary between superficialis and profundus can-
not be determined, but as in the bears the posterior
part of the superficial layer is innervated by the
medial anterior thoracic nerve.
Along its posterior border the superficial sheet
is folded sharply under and continued forward as
a deeper layer (the profundus) immediately be-
neath the superficial one. Thus a very deep and
well-marked pectoral pocket, open anteriorly and
closed posteriorly, is formed.
The superficial sheet arises from the entire ma-
nubrium and from the corpus sterni back to the
level of the eighth sternal rib. The fibers converge
toward the humerus, and insert into the pectoral
ridge in a narrow line along the middle half of the
bone. In other carnivores (including the bears)
insertion is into the deltoid ridge. In Ailuropoda
the proximal end of the insertion line deviates
slightly from the pectoral ridge toward the del-
toid ridge, but by no means reaches the latter.
Probably the tremendous development of the del-
toid and lateral triceps in the panda has crowded
the superficial pectoral off the deltoid ridge and
forward onto the pectoral ridge.
M. sternohumeralis profundus is a narrow
band anterior to the superficial sheet. It arises
from the anterior end of the manubrium, increases
in width as it passes toward the shoulder along the
anterior border of the superficial sheet, and inserts
on the lateral surface of the humerus immediately
below the greater tuberosity, in a line that con-
tinues proximad from the insertion of the super-
ficial sheet. The lateral anterior thoracic nerve and
its accompanying blood vessels pass through the
split between this muscle and the supei-ficialis.
M. pectoralis profundus (figs. 89, 133) lies
mostly beneath the supei-ficialis, although as stated
above its posterior edge is folded forward and fused
with the posterior border of the superficialis. It is
by far the widest element of the pectoral complex.
It is not divisible into anterior and posterior parts.
Origin is from the corpus sterni posteriorly, deeper
fibers arising from the sternal cartilages, from the
eighth forward to the third. At the anterior level
of the third and fourth sternal cartilages the mus-
cle arises wholly from the cartilages, none of the
fibers reaching the sternebrae. The most poste-
rior fibers are joined on their under side by the
panniculus. Insertion extends almost the entire
length of the humerus, beginning proximally on
the greater tuberosity at the edge of the bicipital
groove, and continuing distad on the pectoral ridge
to within 60 mm. of the distal end of the humerus.
M. pectoralis abdominalis (fig. 89) is a nar-
row thin band lying posterior to the profundus.
It arises from the rectus sheath at the level of the
costal arch, passes beneath the posterior edge of
the profundus, and inserts with the panniculus on
the deep surface of the profundus, not reaching the
bicipital arch. The abdominalis is degenerate.
M. subclavius is entirely wanting.
M. serratus ventralis (magnus or anterior of
some authors) and M. levator scapulae (fig. 86)
form a perfectly continuous sheet, so that the
boundary between them cannot be determined.
The common muscle arises from the atlas and all
DAVIS: THE GIANT PANDA
161
succeeding cervical vertebrae, and by fleshy fibers
from the first nine ribs. The sHp arising from the
fifth rib lies over the scalenus; those farther for-
ward lie beneath it. Insertion is made along the
inner surface of the whole vertebral border of the
scapula.
Mm. intercostales externi (figs. 87, 89). The
fibers of these muscles run craniodorsad as far back
as the eleventh rib. Between the eleventh and
fourteenth ribs they run nearly horizontally. The
muscles reach the costal cartilages of all but the
first two ribs, although the intercostales interni
are exposed medially as far back as the seventh
rib. The part of the muscle between the ribs is
fleshy anteriorly, becoming quite tendinous poste-
riorly. Between the costal cartilages this ai'range-
ment is reversed, the muscles being tendinous an-
teriorly and fleshy posteriorly.
A small group of fibers arises from the first costal
cartilage near the manibrium and inserts on the
inner face of the tendon of the rectus. The dorsal
edge of the muscle forms a raphe with the inter-
costal fibers lying dorsad of it, and the fiber direc-
tion is more vertical than that of the intercostales.
It is not known whether this represents a part of
the intercostalis internus or not.
Mm. intercostales interni (figs. 87, 90) are,
as usual, more extensive than the external inter-
costals. They occupy all the space between the
ribs and the costal cartilages. The fibers take the
usual forward and downward direction.
M. supracostalis (fig. 86) is a narrow band
arising from the fourth rib. Running anteriorly
closely applied to the ventral edge of the scalenus,
it swings ventrad to insert on the costal cartilage
of the first rib.
M. transversus thoracis (fig. 90) is a thin
sheet, more or less divisible into separate bands,
that occupies the space between the third and
eighth sternal cartilages on the inner side of the
thoracic wall. Origin is from all the sternal seg-
ments except the first two and from the anterior
third of the xiphoid cartilage, and insertion is
made on the sternal cartilages and aponeurotically
on the fascia covering the inner surface of the in-
ternal intercostals.
A narrow ribbon of muscle arises from the third
sternal segment and passes forward to insert apo-
neurotically into the fascia of the intercostals. It
is not known whether this represents a part of the
transversus thoracis or not.
M. diaphragma (fig. 90). Pars lumbalis is di-
vided into three crura. Crus laterale, which is the
largest of the three, has a double origin. The lat-
eral fibers arise by means of a stout tendon from
the ventrolateral surface of the third lizmbar ver-
tebra. Medial fibers arise, at the level of the sec-
ond lumbar vertebra, from the lateral edge of a
long tendon that runs cephalad from the ventral
surface of the fourth lumbar vertebra. This ten-
don runs forward along the medial border of the
pars lumbalis as far as the aortic notch, and gives
rise to all the remaining fibers of this part of the
diaphragm. On the deep surface of the lateral
crus some of the fibers also arise directly from the
second lumbar. Crus intermedium is very narrow.
It is separated from the lateral crus throughout
almost its entire length by a branch of the phrenic
nerve, while its medial border slightly overlaps
the lateral border of the medial crus. It arises
from the medial tendon mentioned above, at the
level of the anterior border of the second lumbar
vertebra, its origin being continuous with that of
the lateral crus. Crus mediale arises from the me-
dial tendon at the level of the posterior border of
the first lumbar vertebra, its origin being continu-
ous with that of the intermediate crus. The me-
dial crus fuses with its fellow of the opposite side
cephalad of the hiatus aorticus, which is situated
below the thirteenth thoracic vertebra.
Pars costalis arises from the ninth to the eleventh
costal cartilages by a series of interdigitations with
the transversus abdominis. These interdigitations
do not correspond perfectly in number with the
ribs, some costal cartilages receiving more than
one digitation each; nor do the digitations corre-
spond exactly on either side of the sternum.
Pars sternalis arises from the lateral border of
the posterior part of the elongate xiphoid process.
It is a narrow band that promptly joins the adja-
cent medial border of the pars costalis.
2. Muscles of the Abdomen
M. rectus abdominis (figs. 86, 87, 89, 91) ex-
tends as a thin, rather narrow, band from the pel-
vic symphysis to the first costal cartilage. It
reaches its greatest width of 100 mm. at about the
level of the sixth sternal cartilage. Tendinous in-
scriptions are absent. The muscle arises by fleshy
fibers, covered by a heavy aponeurosis, from the
posterior part of the pelvic symphysis, the origin
extending anteriorly along the ventral midline. A
few of the fibers nearest the midline insert into the
linea alba just behind the xiphoid cartilage. Suc-
cessive slips farther laterad insert on the fifth, sixth
and seventh costal cartilages, and slightly less than
the lateral half of the muscle is continued forward,
to insert by a wide tendon on the first costal carti-
lage. This tendon begins at the level of the third
costal cartilage. The rectus does not participate
in the formation of the inguinal canal.
M. atiantoscapularis
(cut)
M. acromiotiap. (cut)
M. levator scapulae vent.
M. cephalohumer.
M. acromiodclL
M. brachialis
M. atiantoscapularis
M. triceps lateralis
M. triceps longus
. dca-so-epitrochlearis
M. spinodeltoideus
'M. acromiotrap.
M. spinotrap.
M. obliquus abdom. extemus
M. vastus lateralis
M. qxiadratus femoris
M. adductor
M. semimembranosus
M. semitendinosus
M. tenuissimus
Fascia lumbodorsalis superf.
M. glutaeus superf.
M. tensor fasciae latae
M. semimonbranoeus
M. biceps femoris
Fig. 88. Dorsal view of body musculature of Ailuropoda, superficial layer on right, deeper layer on left.
162
M. omohyoideus
M. stemocleidomastoideus '
M. cephalohumer.
M. stemohumer. prof,
M. pect. superf,
Hyoid
M. th}rreohyoideus
M. cricothyreoideus
M. stemothyreoideus
M. stemohyoideus
M. rectus abdominis
(cut)
M. vastus med.-
M. sartorius
M. adductor
M. semimembranoeus
M. gracilis
M. aemitendinosus
M. intercost. ext
M. obliquus intemus
M. tensor fasciae latae
M. iliopsoas
M. adductor
M. vastus med.
M. rectus femoris
v M. adductor
M. aonimembranoeut
M. aemitendinosus
Fig. 89. Ventral view of body musculature of Ailuropoda, superficial layer on right, deeper layer on left.
163
164
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
M. sternohyoideus +
M. stemothyreoideus
M. stemomastoideus
A. & V. mammaria int.
M. transv. thoracis
M. intercost. int,
M. diaphragma,
pars sternal is
Proc. xiphoideus
M. diaphragma^
pars costal is
M. transversus
abdominis
Fig. 90. Ventral wall of thorax of Ailuropoda, internal view.
M. obliquus abdominis externus (figs. 86, 88,
89, 91) arises by short tendons from the fourth to
the ninth ribs, and by fleshy fibers from the tenth
to the thirteenth. Apparently none of the fibers
reach the dorsal fascia. Posterior to the serratus
ventralis the obliquus attaches to the ribs (10-13)
immediately behind the origins of the latissimus
dorsi. It is difficult to determine whether the
fibers dorsal to the origins of the latissimus rep-
resent continuations of the obliquus or whether
they are external intercostals, as the fiber direc-
tion is exactly the same. When the dorsal border
of the obliquus is lifted, however, the muscle sheet
dorsal to it is found to be perfectly continuous
with the intercostals lying beneath the obliquus.
Insertion: the muscle fibers slightly overlap the
lateral edge of the rectus before giving way to the
tendinous aponeurosis that extends over the rectus
to the linea alba at the ventral midline (the rec-
tus sheath). In the inguinal region the aponeu-
rosis expands into a large triangular sheet, the
abdominal tendon (see below), which inserts into
the posterior third of the inguinal ligament.
DAVIS: THE GIANT PANDA
165
M. obliquus abdom. ext.
M. aartoriua
Vagina m.
red. abdom.
M. obLabd.
int (cut &
red.)
Eminentia
Uiopeetinea
M. obL
abd.ext.
[Tendo abd]
(cut & rea)
Aimulus iniuimU int.
M. adductor
Tertdo praepubieu*
Tendo praepubicus
gracilis
Fig. 91. The inguinal region of At'/Mropoda. The dotted line shows the position of the internal inguinal ring. The arrows
pass through the lacuan musculo-vasorum (lateral) and inguinal canal (medial).
M. obliquus abdominis internus (fig. 87, 89,
91) is much less extensive than the externus. It
is rather sharply divided into two parts: an ante-
rior division (pars costalis) that inserts on the last
ribs, and a more extensive posterior part (pars
abdominalis+pars inguinalis) that inserts aponeu-
rotically into the ventral belly wall. These two
divisions are separated by a considerable gap ven-
trally. The anterior division arises from the crest
of the ilium from the anterior superior iliac spine
mesad nearly to the middle of the crest, and from
the iliac end of the inguinal ligament, and inserts
on the last three ribs. The posterior division arises
exclusively from the inguinal ligament. Posteri-
orly the fibers run almost vertically downward, or
may even run slightly ventrocaudad ; anteriorly
they run diagonally forward and downward. The
muscle terminates in a tendinous aponeurosis that
participates in the formation of the rectus sheath
(see below). This aponeurosis is more extensive
anteriorly, where the muscle fibers fail by 40 mm.
to reach the edge of the rectus. Posteriorly the
muscle fibers extend to the edge of the rectus. In
the inguinal region the internal oblique is perforated
by the inguinal canal.
M. transversus abdominis (figs. 87, 89, 90,
91) arises from the cartilages of the last six ribs,
interdigitating with the origins of the diaphragm.
Additional origin is taken from the lumbodorsal
fascia, from the tip of the ilium, and from the an-
terior end of the inguinal ligament. The muscle
terminates in a tendinous aponeurosis that fuses
with the inner layer of the aponeurosis of the in-
ternal oblique to form the inner sheath of the rec-
166
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
tus. The posteriormost fibers insert into the lateral
third of the iliac crest.
M. cremaster (fig. 91) arises as a fine tendon
from the inguinal ligament 25 mm. anterior to the
internal inguinal ring. The tendon takes accessory
origin from the transverse fascia on its way to the
inguinal canal. As it enters the canal the tendon
fans out into a band of muscle fibers that passes
through the canal dorsad of the spermatic cord,
and expands to form the cremasteric fascia around
the tunica vaginalis of the testis.
M. quadra tus lumborum (fig. 100) is a com-
plex muscle arising from the last three thoracic
vertebrae and ribs and the transverse processes of
all the lumbar vertebrae. Insertion is into the
transverse processes of the lumbars and the in-
ternal lip of the iliac crest for about its middle
third and the adjacent inferior surface of the ilium.
3. The Inguinal Region. Figure 91.
The structures in the inguinal region are some-
what modified in Ailuropoda, in comparison with
related carnivores, because of the extremely short
pelvic symphysis.
The abdominal tendon [Bauchsehne+Becken-
sehne of German veterinary anatomists] is the in-
sertion aponeurosis of the external oblique muscle.
Anteriorly the aponeurosis of this muscle passes
into the outer rectus sheath, while in the inguinal
region it forms a large triangular sheet that fills
the angle between the linea alba and the inguinal
ligament. The aponeurosis is perforated by the
inguinal canal ; the part anterior to this perforation
is the "abdominal tendon," the part posterior to
it the "pelvic tendon" of the German anatomists.
The aponeurosis inserts into the posterior third
of the inguinal ligament, from the level where the
femoral vessels emerge back to the symphysis.
The lamina femoralis, which in the dog and other
domestic quadrupeds splits off from the abdominal
aponeurosis at the lateral border of the inguinal
ring and runs onto the medial surface of the thigh,
appears to be wanting in Ailuropoda.
The prepubic tendon is a heavy, compact liga-
ment extending from the iliopectineal eminence
back to the anterior border of the pelvic symphy-
sis, where it meets its mate of the opposite side.
The tendon is more or less continuous with the in-
guinal ligament anteriorly. It lies superficial to
the pectineus muscle, and arises chiefly from the
origin tendon of that muscle. Where it passes over
the origin tendon of the gracilis near the symphy-
sis, the prepubic tendon is inseparably fused with
the tendon of that muscle. The tendon provides
attachment for the linea alba and the posterior-
most fibers of the internal oblique.
The inguinal ligament lies at the juncture of
the medial surface of the thigh and the wall of the
abdomen. It extends from the anterior iliac spine to
the iliopectineal eminence. Beyond the eminence
it is continued posteriorly as the prepubic tendon.
As in other quadrupeds, the inguinal ligament is
poorly defined in Ailuropoda. Anteriorly it is little
more than a fiber tract from which the posterior
fibers of the internal oblique take origin. Poste-
riorly, where it bridges over the lacuna musculo-
vasorum, it is a heavier and more sharply defined
ligament.
Between the inguinal ligament and the ventral
border of the pelvis there is a large gap, the lacuna
musculovasorum (lacuna musculorum + lacuna
vasorum of human anatomy; the iliopectineal liga-
ment, which separates these in man, is wanting in
quadrupeds). Through this opening the iliopsoas
muscles and the femoral vessels and nerve pass
from the abdominal cavity onto the thigh. In
Ailuropoda (as in the dog) the femoral vessels lie
ventrad of the iliopsoas, rather than posterior to it,
and no true femoral ring can be distinguished.
The lacuna is about 50 mm. long.
The inguinal canal is very short, its length
being little more than the thickness of the abdom-
inal wall. It is about 12 mm. long, and is directed
posteriorly and slightly medially. It is situated
about 30 mm. in front of the pelvic symphysis.
The inlet to the canal, the internal inguinal ring,
is formed by a hiatus in the internal oblique mus-
cle; the anterodorsal border, between the limbs of
the opening in the muscle, is formed by the in-
guinal ligament. The rectus abdominis does not
participate in forming the medial border of the
ring, as it does in the dog. The internal ring meas-
ures about 30 mm. in long diameter. The outlet,
the external inguinal ring, is associated with the
abdominal tendon of the external oblique. In the
inguinal region this sheet splits to form the lateral
and medial limbs of the ring. The fibers of the
lateral limb radiate into the origin tendon of the
pectineus and the prepubic tendon, while the fibers
of the medial limb pass into the rectus sheath.
The ring is completed posterodorsally by the pre-
pubic tendon; i.e., the two limbs do not re-unite
posteriorly, but merely form a ventral arch around
the spermatic cord.
The sheath of the rectus abdominis is formed
externally by the aponeurosis of the external
oblique fused with the ventral layer of the apo-
neurosis of the internal oblique. Internally the
sheath is formed by the dorsal layer of the aponeu-
rosis of the internal oblique fused with the apo-
neurosis of the transversus abdominis. Thus the
rectus muscle is embraced between the dorsal and
DAVIS: THE GIANT PANDA
167
ventral layers of the internal oblique aponeurosis.
In the dog the inner layer of the rectus sheath
". . . is formed for the most part by the terminal
aponeurosis of the transversus abdominis . . . and
in the anterior portion in addition by an inner
layer of the terminal aponeurosis of the obliquus
abdominis internus." (Baum and Zietzschmann.)
The inguinal region of Ailuropoda differs from
that of the dog (Baum and Zietzschmann; the only
other carnivore in which this region is known) in
several respects. The following peculiarities of the
giant panda may be mentioned:
(1) The rectus does not participate in the for-
mation of the inguinal canal.
(2) The rectus inserts into the posterior part of
the symphysis.
(3) The cremaster does not arise from the pos-
terior border of the internal oblique.
(4) The abdominal tendon of the external
oblique does not form the entire circum-
ference of the external inguinal ring.
I^. Muscles of the Back
Superficial Secondary Back Muscles. M.
cephalohumeralis (= clavodeltoideus +clavotra-
pezius) (figs. 88, 134) is powerfully developed. Near
its insertion it has a thickness of about 20 mm.
Its origin, which is continuous with that of the
acromiotrapezius, extends on the lambdoidal crest
from the level of the dorsal border of the zygoma
to the dorsal midline, then by aponeurosis from
the ligamentum nuchae for 90 mm. along the mid-
line of the neck. The anterior border is slightly
overlapped by the temporalis. The fibers converge
over the anterior border of the shoulder, and insert
fleshily into the lower half of the deltoid ridge and
the area between this ridge and a second ridge
midway between the deltoid and pectoral ridges.
At its insertion the muscle forms a partial raphe
with the acromiodeltoid laterally and with the
pectoralis superficialis and profundus medially.
The clavotrapezial part of the cephalohumeral
is innervated by the spinal accessory, and the
clavodeltoid part by the axillary nerve.
Action: Chief extensor of the fore leg.
M. acromiotrapezius (figs. 88, 134) is a thin,
rectangular sheet arising from the dorsal midline
by a long, broad aponeurotic sheet; fleshy fibers
appear as the muscle crosses the scapular border.
The muscle is thus sharply divided into two parts,
a fleshy part lying over the scapula and an aponeu-
rotic part between the vertebral border of the
scapula and the dorsal midline. Its origin is con-
tinuous with the aponeurotic origin of the cephalo-
humeral anteriorly, and extends a distance of
110 mm. along the dorsal midline. The fleshy
part of the muscle has a length of only 70 mm.
Insertion is made for a distance of 105 mm. into
the humeral half of the scapular spine.
M. spinotrapezius (figs. 88, 134) is triangular
in outline. The anterior border is sharply con-
cave, so that a portion of the underlying rhom-
boids and supraspinous fascia is exposed between
this muscle and the acromiotrapezius. The pos-
terior edge is concave and thin, but the muscle
becomes quite heavy anteriorly. Origin is from
the spinous processes of the thoracic vertebrae for
a distance of 160 mm. The anterior border is over-
lapped slightly by the acromiotrapezius near the
midline. The fleshy part of the muscle stops
abruptly at the posterior border of the scapula,
and the muscle continues forward and downward
across the scapula as a wide, heavy aponeurosis
that inserts into the superficial fascia of the infra-
spinatus. Thus the condition in the spinotrapezius
is the reverse of that in the acromiotrapezius,
where the part of the muscle lying over the scap-
ula is fleshy and the part beyond the scapula is
aponeurotic.
The relations of fleshy and aponeurotic parts of
the acromio- and spinotrapezius to the underlying
scapula in Ailuropoda appear to be pressure phe-
nomena. Similar conditions are known from human
anatomy, e.g., the digastric. It is noteworthy,
however, that the trapezius is almost exactly the
same in the Ursidae (verified in our specimens of
Selenarctos and Tremarctos), and is surprisingly
similar, considering the difference in body size and
proportions, in Ailurus. The development of these
extensive aponeurotic sheets is even indicated in
Bassariscus and Procyon. The dogs, on the other
hand, show nothing comparable to it, nor do
other carnivores, including such large forms as
the hyenas and lion.
Action: The trapezius muscles elevate the scap-
ula and rotate it counterclockwise.
M. latissitnus dorsi (figs. 88, 134) is very pow-
erfully developed. It has the customary triangu-
lar form. The anterior border is overlapped by
the spinotrapezius. It arises mostly by aponeuro-
sis from the mid-dorsal line, fleshy fibers reaching
the midline only at a point just behind the spino-
trapezius. Ventrally and ventro-posteriorly the
muscle takes origin from the seventh to eleventh
ribs. Origin from the seventh rib is limited to a
very few fibers, but the origin from each successive
rib increases in length until on the eleventh it ex-
tends over 95 mm. The fibers converge toward the
axilla, and insertion is made by two heads. The
smaller head inserts chiefly into the inner face of
168
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
the panniculus carnosus, a few of the most poste-
rior fibers reaching the epitrochlearis. The main
mass of the muscle forms a powerful raphe with
the epitrochlearis, and these two muscles make a
common insertion into the tendon of the teres
major.
Action: Chief flexor of the arm.
M. rhomboideus (figs. 86, 88, 92, 134) is more
or less divisible into two parts. The muscle is
elongate triangular in outline, and arises in a con-
tinuous line from the lambdoidal crest at about the
level of the dorsal border of the zygoma up to
the dorsal midline, then back for 270 mm. along the
midline of the neck. The muscle may be separated,
particularly near its insertion, into anterior and
posterior masses, of which the posterior is much
the more extensive. Insertion is made into the
dorsal half of the coracoid border and entire ver-
tebral border of the scapula. The anterior edge
of the posterior part lies partly over that of the
anterior.
Action: Draws the scapula toward the verte-
bral column.
M. occipitoscapularis (rhomboideus anterior
or capitis of authors) (fig. 134) is a narrow band
arising from the lambdoidal crest. The muscle
runs backward, separated from the rhomboideus
by the dorsal branch of the A. and V. transversa
colli, to insert on the coracovertebral border of
the scapula, beneath the insertion of the anterior
part of the rhomboideus.
Action : Draws the scapula forward.
M. atlantoscapularis (levator scapulae ven-
tralis of authors; omo-cleido-transversarius of Carl-
sson) (figs. 86, 134) is a narrow, heavy band arising
from the transverse process of the atlas. For a
short distance it is inseparable from the first digi-
tation of the levator scapulae, with which it has
a common origin. Immediately distad of its origin
it is easily separable into two subequal parts, which
embrace a branch of the fourth cervical nerve be-
tween them. This separation loses its identity
near the insertion, which is made, by means of a
short fine tendon, into the metacromion of the
scapula, at the juncture of the acromiodeltoideus,
the spinodeltoideus, and the acromiotrapezius.
M. serratus dorsalis anterior (fig. 86) arises
by fleshy slips from the posterior borders of the
fifth to tenth ribs. The fibers from these six ori-
gins more or less unite to form a continuous sheet
that inserts aponeurotically into the dorsal fascia.
M. serratus dorsalis posterior (fig. 86) is lim-
ited to two slips. The more anterior of these
arises from the twelfth rib; the posterior from the
thirteenth, with a few fibers coming from the four-
teenth. The fibers run straight dorsad, to insert
independently of one another into the dorsolum-
bar fascia by means of aponeuroses.
Deep Intrinsic Back Muscles. M. splenius
(figs. 86, 87, 92) is very powerfully developed, par-
ticularly along its lateral border, where it attains
a thickness of 15 mm. Posteriorly the muscle
arises by a wide tendinous aponeurosis from the
dorsoliunbar fascia at about the level of the fifth
thoracic vertebra; this aponeurosis lies beneath the
origin of the serratus posterior superior. Origin,
by a similar aponeurosis, is taken along the mid-
line as far forward as the lambdoidal crest of the
skull. This medial aponeurosis has a width of
15-20 mm. Insertion is made on the lambdoidal
crest, just beneath the insertion of the rhom-
boideus, and from the mastoid process down to
its tip. Tendinous intersections are absent.
The usual undifferentiated muscle mass occu-
pies the trough formed by the spines and trans-
verse processes of the lumbar vertebrae. At the
level of the last rib it divides to form three mus-
cles: the iliocostalis, the longissimus, and the spi-
nalis. The medial part of the muscle mass is
covered with a heavy aponeurosis, which gives
rise to many of the superficial fibers of all three
muscles.
M. iliocostalis (figs. 87, 88, 92) is the most lat-
eral of the superficial back muscles. It gives off a
tendinous slip to each of the ribs near its angle
and to the transverse process of the last cervical
vertebra. The more posterior tendons pass over
one rib before inserting, those farther forward over
two. Slips from all the ribs except the first four
join the muscle as it runs craniad.
M. longissimus (figs. 87, 88, 92) is the middle
one of the three superficial back muscles. There
is no demarcation between the pars dorsi and pars
cervicis of human anatomy. On the other hand,
the muscle is sharply divided into a lumbar part
(M. ilio-lumbalis [Virchow], Pars lumborum m.
longissimus dorsi [Winckler], M. longissimus lum-
borum [Eisler]), arising from the ilium and covered
by the heavy deep layer of the lumbar fascia; and
a thoracic part. The thoracic part arises from the
lumbar fascia, and farther anteriorly from the
fascia between itself and the spinalis. There is
the usual double insertion: medially by fasciculi
into the anapophyses of the lumbar and thoracic
vertebrae, and laterally by long tendons into all
but the last four ribs and into the transverse proc-
esses of the last six cervical vertebrae.
M. longissimus capitis (fig. 92) arises from the
transverse processes of the last three cervical ver-
DAVIS: THE GIANT PANDA
169
M. multifidus
Vertebra thoraaUis I
Nn. cervicales doraales
M. splenitis (cut)
M. rectus capitis
dorsalis major (cut)
w ,,. ... . \x -^"- biventer cervicus I M. rhomboideus (cut)
M. oWiquus capitis post. \\ et complejcus '
M. multifidus cervicis \ \\ m. rectus capitis^
Axis-Proc. spiMlis\ \ \ dorsalis mediusN
Coital
M. rectus capitis lateralis'
M. rectus capitis
dorsalis minor
M. obliquus capitis ant.
Fig. 92. Deep muscles of neck and anterior thorax of Ailuropoda, right side.
tebrae. It is composed of two very slender heads.
One of these joins the ventral border of the sple-
nius in the usual way, and thus inserts into the
mastoid process. The other head, which comes
from the anterior fibers of the common origin, lies
deep to the splenius along the ventral border of
the complexus, inserting with it into the occipi-
tal bone.
M. longissimus atlantis (fig. 92) is slightly
larger than the combined heads of the longissimus
capitis. It arises from the articular pi-ocesses of
the third, fourth, and fifth cervicals, and inserts
into the tip of the wing of the atlas.
M. spinalis dorsi (figs. 87, 88) is the most me-
dial and most extensive of the superficial back
muscles. It is present only in the thoracic region.
Origin is from the anterior edge of the deep lumbar
fascia, and farther anteriorly from the fascia be-
tween itself and the longissimus. The fibers run
diagonally craniad and mesad, and insert, by ten-
dons that become progressively longer, anteriorly
into the tips of the spinous processes of all the
thoracic and the first cervical vertebrae.
M. semispinalis is represented only by the
capitis, which is separable into a dorsal biventer
cervicis and a ventral complexus. M. biventer
cervicis (fig. 92) has three diagonal tendinous in-
tersections. The muscle begins at the level of the
fifth thoracic vertebra, arising posteriorly from a
wide aponeurotic fascia that covers the underly-
ing muscles. Additional origin is taken by means
of tendinous fasciculi from the tips of the spines
of the fourth, third, and second thoracics, and an-
terior to this from the ligamentum nuchae, as well
as from the transverse processes of the second to
fifth thoracics. Insertion is fleshily into the occipi-
tal crest near the dorsal midline. M. complexus
lies beneath the biventer cervicis posteriorly. It
begins at the level of the second thoracic vertebra,
arising posteriorly from an aponeurotic fascia sim-
ilar to that of the biventer. Additional origin is
taken from the transverse processes of the first two
thoracic and last four cervical vertebrae. Inser-
tion is made, by mingled fleshy and tendon fibers,
into the medial half of the occipital bone. The
muscle lies partly deep to the biventer cervicis at
its insertion.
M. multifidus (fig. 92) is continued craniad
from the extensor caudae medialis. In the lum-
bar region it is deep to the spinalis. The muscle
is, as usual, best developed in the lumbar region,
where it is not separable into individual fasciculi;
at the anterior end of the deep lumbar fascia it is
fused with the spinalis. In the thoracic region the
multifidus is more or less separable into fasciculi,
which arise by mingled tendon and muscle fibers
from the transverse processes of the vertebrae and
pass forward over one vertebra to insert on the
spinous process of the next. M. multifidus cervicis
is well developed, consisting of three bundles of
longitudinal fibers extending between the articular
processes and the spines of the cervical vertebrae.
M. rectus capitis dorsalis major (fig. 92) is a
rather thin triangular muscle arising from the an-
170
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
terior two-thirds of the crest of the spine of the
axis, and inserting into the occipital bone below
the lambdoidal crest. The muscles from either
side diverge as they leave the axis, so that a tri-
angular cavity, bounded ventrally by the atlas
and filled with fat, remains between their medial
borders.
M. rectus capitis dorsalis medius (fig. 92)
is apparently represented by a few fibers, super-
ficial to the medial fibers of the rectus minor and
with a less oblique fiber direction, that arise from
the anterior tip of the spine of the atlas and follow
the border of the triangular cavity described above,
to insert with the rest of the rectus on the skull.
M. rectus capitis dorsalis minor (fig. 92) lies
partly beneath and partly laterad of the medius.
It is a large muscle with the usual origin from the
anterior border of the dorsal arch of the axis, and
inserts into the occipital bone beneath the major
and medius.
M. rectus capitis lateralis (fig. 92) is a rela-
tively small muscle lying along the ventral border
of the obliquus capitis anterior. Origin is from
the ventral surface of the tip of the wing of the
atlas, deep to the origin of the rectus capitis ven-
tralis. The muscle expands somewhat toward its
insertion, which is made into the posterior surface
of the mastoid process near its outer edge.
M. obliquus capitis anterior (fig. 92) is also
relatively small. It is triangular in outline, arising
from the tip of the wing of the atlas and insert-
ing into the back of the skull just above the mastoid
process. The dorsal edge of the muscle is overlain
by the second head of the longissimus capitis.
M. obliquus capitis posterior (fig. 92) greatly
exceeds the anterior in size. Origin is from the
entire spinous process of the atlas. The fiber direc-
tion is nearly vertical. Insertion is into the wing
of the atlas.
5. Muscles of the Tail. Figure 93.
M. extensor caudae medialis is the posterior
continuation of the multifidus, and is in contact
with its mate along the dorsal midline. Origin is
from the spinous processes of the last two lumbar
vertebrae and from the spine of the sacnun. Inser-
tion is into the prezygapophyses (on the anterior
vertebrae) and dorsal surfaces (posterior vertebrae)
of the caudals from the second on, by tendons that
unite with the tendons of the extensor caudae lat-
eralis.
M. extensor caudae lateralis arises from the
deep surface of the deep lumbar fascia, from the
fused transverse processes of the sacral vertebrae,
and from the transverse processes (or bodies, where
these are absent) of the caudal vertebrae. Long
tendons extend posteromesad over three vertebrae,
uniting with the tendons of the extensor caudae
medialis.
M. abductor caudae externus arises from the
dorsal surface of the fused transverse processes of
the sacrum, from the fascia surrounding the base
of the tail, and from the transverse processes of
the first four caudals; there is no attachment to the
ilium. Insertion is into the transverse processes
(or the sides) of the three following vertebrae.
M. abductor caudae internus is a relatively
small fusiform muscle lying ventrad of the exter-
nal abductor. Origin is by a rather wide, flat
tendon that splits off from the tendon of the ilio-
caudalis, thus coming from the medial surface of
the ilium. Insertion is into the transverse proc-
esses of the first six caudals, in common with the
insertions of the external abductor.
M. iliocaudalis is a thin triangular sheet. Ori-
gin, by means of a wide tendinous sheet externally
and fleshy fibers internally, is from the medial sur-
face of the iliimi caudad of the sacro-iliac articula-
tion. A long terminal tendon from the fusiform
part of the muscle joins a tendon of the medial
division of the flexor caudae longus, to insert into
the ventral side of the sixth caudal. The remain-
der of the muscle inserts fleshily into the trans-
verse processes of the posterior sacral and first two
caudal vertebrae.
M. pubocaudalis is a very wide, thin sheet ly-
ing immediately external to the levator ani. The
dorsal fibers arise from the tendon of the iliocau-
dalis, the ventral fibers from the dorsal (inner)
surface of the symphysis pelvis. Insertion is into
the ventral surfaces of the fourth and fifth caudals.
M. flexor caudae longus is composed of two
sets of fasciculi, which are separated proximally by
the iliolumbalis. The lateral division consists of
successive fasciculi arising from the posterior end
of the sacrum and from the transverse processes
(or sides) of the caudal vertebrae. The strong ter-
minal tendons pass over three vertebrae before
inserting into the transverse process (or side) of
the fourth succeeding vertebra. The medial divi-
sion arises just mesad of the lateral division. It
extends from the anterior end of the sacrum to
the third caudal vertebra, and its ventral edge is
partly united to the adjacent edge of the iliocau-
dalis. It is composed of three successive fasciculi,
each of which terminates in a tendon. The tendon
of the most anterior fasciculus joins the much
stouter tendon of the middle fasciculus; together
they insert with the pubocaudalis into the ventral
surface of the fifth caudal. The tendon of the most
posterior fasciculus joins a tendon of the long flexor,
and inserts into the ventral side of the sixth caudal.
u
4->
B
>
a
3
O"
o
o
a
o
s
I
s
o
s
171
172
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
M. flexor caudae brevis consists of short fas-
ciculi lying along the ventral midline from the fifth
caudal on. Origin is from the ventral surface of
the vertebra, and the fibers pass over one vertebra
to insert into the next.
6. Muscles of the Perineum
M. levator ani is a thin triangular sheet of
muscle lying deep to the coccygeus, and over the
lateral surfaces of the rectum and urethra. Its
fiber direction is at right angles to that of the coc-
cygeus. Origin is chiefly by means of a thin apo-
neurosis from the medial surface of the ascending
ramus of the pubis; some of the posterior fibers are
continued from the retractor penis, and some are
blended with the sphincter ani externus. Insertion
is into the centra of the anterior caudal vertebrae.
M. sphincter ani externus is a narrow ring of
muscle fibers sun'ounding the anus. The two halves
of the muscle meet below the anus and immedi-
ately behind the bulbus urethrae; some of the fibers
are continued into the suspensory ligament of the
penis, which attaches to the posterior end of the
symphysis; others attach to the bulbus urethrae
and ischiocavernosus.
M. ischiocavernosus is a very short muscle
arising from the posterior border of the ischium,
25 mm. above the symphysis. It is closely applied
to the posterior wall of the corpus cavernosum
penis, and terminates by spreading out over this
structure.
M. bulbocavernosus is a thin layer of diag-
onal muscle fibers surrounding the bulbus iirethrae.
The two muscles arise from a median raphe on the
ventral side, and insert into the posterior part of
the root of the penis.
M. sphincter urethrae membranaceae is a
delicate layer of transverse muscle fibers surround-
ing the urethra proximad of the bulb. It encases
the urethra for a distance of 30 mm.
M, retractor penis is a pale muscle arising as
a continuation of fibers from the levator ani. It
meets its mate from the opposite side just below
the rectum, and the two muscles run side by side
to the base of the glans penis, where they insert.
A few fibers split off and insert into the side of the
radix penis.
M. caudorectalis is a prominent unpaired mus-
cle lying along the midline in the anal region. It
is distinctly lighter in color than the surrounding
musculature. Origin is from the dorsal side of the
rectum in the midline. The fibers pass backward
and upward as a fusiform mass, to insert on the
ventral surface of the sixth caudal vertebra.
III. MUSCLES OF THE FORE LEG
A. Muscles of the Shoulder Girdle
M, supraspinatus (figs. 88, 95, 96, 133) is cov-
ered externally by the usual heavy tendon-like
fascia, which cannot be detached without cutting
into the muscle substance. This tendinous fascia
is continued diagonally downward to insert on the
acromion process, immediately behind the origin
of the acromiodeltoideus; the fascia over the distal
end of the muscle is normal. The muscle occupies
the whole of the supraspinous fossa, overlapping
the cephalic border. It is powerfully developed,
having a maximum thickness of 50 mm. Insertion
is by fleshy fibers into the greater tuberosity of
the humerus.
Action: Extends the arm on the scapula.
M. infraspinatus (fig. 95) arises from the entire
infraspinatus fossa. It is covered with a tendinous
aponeurosis down to the origin of the spinodel-
toideus. The muscle is divisible into two parts,
the one nearest the glenoid border of the scapula
being slightly the smaller. The insertion tendons
of the two parts are more or less distinct, but are
fused where they are in contact. Insertion is into
the prominent infraspinatus fossa on the greater
tuberosity of the humerus.
Action: Chief lateral rotator of the arm. Its
tendon acts as a lateral collateral ligament of the
shoulder joint.
M. acromiodeltoideus (figs. 88, 95, 134) is
powerfully developed, having a thickness of 23 mm.
at its posterior edge. It is covered with tendinous
fascia superficially. The muscle arises, partly flesh-
ily and partly tendinously, from the whole tip of
the acromion. It is bipennate, to two halves of
approximately equal width. Insertion is by two
heads, which correspond to the halves of the bi-
pennate muscle. The anterior half inserts on the
shaft of the humerus immediately above the in-
sertion of the cephalohumeral, anterior to the del-
toid ridge. The posterior part inserts partly on
the lateral head of the triceps, posteriorly forming
a strong raphe with the spinodeltoid.
Action: Chief abductor of the arm.
M. spinodeltoideus (fig. 88) arises almost
wholly from the fascia of the infraspinatus; only
its anterior tip reaches the scapular spine. Most
of its fibers meet the acromiodeltoideus in a tendi-
nous raphe, although a few insert on the triceps
lateralis.
Action: Flexes the arm.
M. teres minor (fig. 95) is a small muscle,
closely applied to the inferior border of the infra-
I
DAVIS: THE GIANT PANDA
173
spinatus, from which it is inseparable at its origin;
it is not attached to the long head of the triceps.
It arises by heavy aponeurotic fibers that are
firmly attached to the underlying infraspinatus on
the deep surface, from a small area on the axillary
M. subscapularis (figs. 96, 133) is composed of
three main divisions. The two anterior subdivi-
sions are composed of numerous bipennate units,
whereas the posterior one is made up of units with
parallel fibers. Insertion is into the proximal end
Caput humeri
M. eoracobrachialis brevis
M. eoracobrachialis longus
M. biceps (caput longus)
Epicondylut med
M. biceps (caput brevis)
Fig. 94. Right arm of bear (Ursus amerieanus) to show short head of biceps. Medial view.
border of the scapula just proximad of the middle.
Insertion is made by a short stout tendon into the
head of the humerus, immediately distad of the
insertion of the infraspinatus.
Action: Flexes the arm and rotates it laterally.
M. teres major (figs. 95, 96) is powerfully de-
veloped. It arises from the usual fossa at the distal
end of the glenoid border of the scapula, and from
a raphe that it forms with the subscapularis on
one side and the infraspinatus on the other. In-
sertion is made, by means of a powerful flat tendon
30 mm. in width, common to it and the latissimus
dorsi, on the roughened area on the medial surface
of the shaft of the humerus, distad of the bicipital
groove and immediately mesad of the pectoral
ridge. An extensive bursa (Bursa m. teretis major
of human anatomy) is inserted between the ten-
don and the shaft of the humerus.
Action: Assists the latissimus dorsi in flexing
the arm, and the subscapularis in medial rotation
of the arm.
of the humerus, immediately below and behind the
lesser tuberosity. The insertion tendon of the first
(crania) unit is superficial to those of the other two
units.
Action: Chief medial rotator of the arm. The
upper part of the muscle acts as an extensor of
the arm.
B. Muscles of the Upper Arm
M. biceps brachii (figs. 96, 97, 133) is a fusi-
form muscle that, in the position in which the arm
was fixed, is rather sharply flexed at the site of the
bicipital arch. The muscle displays a rather curi-
ous structure. It arises by a single (glenoid) head,
but in the proximal two-thirds of the muscle a
narrow anterior group of fibers is more or less sep-
arable from the main mass of the muscle. These
fibers, which are particularly conspicuous because
they lack the glistening tendinous covering of the
rest of the muscle, arise from the origin tendon of
the biceps as it passes through the bicipital groove
and insert extensively into the anterior surface of
174
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
M. supraspinatus
-Caput humeri
-M. acromiodelt.(cut)
M. infraspinatus
-M. teres minor
M. triceps longus
M. triceps lateralis
M. anconaeus
M. ext. carpi uln.
M. ext. dig. lat.
Caput uln., m. flex dig. prof.
M. ext. indicis proprius
M. ext. dig. com.
Lig. carpi dorsale icuti
Fig. 95. Muscles of the right fore leg of Ailuropoda, lateral aspect.
the main mass of the biceps, as far distad as the
bicipital arch. There was no indication of a short
head in two specimens dissected.
The biceps arises from the bicipital tubercle at
the glenoid border of the scapula, by a long, flat-
tened tendon that runs through the bicipital
groove, enclosed in the joint capsule, onto the ante-
rior surface of the humerus. The tendon is contin-
ued into an extensive area of tendinous aponeurosis
on the external surface of the belly of the muscle,
and a more limited area of similar tissue on the in-
ternal surface. The most medial (superficial) fibers
of the biceps terminate in a well-defined lacertus
fibrosus, which is continued into the fascia over the
pronator teres. The tendon of insertion begins mid-
way on the deep surface of the muscle and continues
distad as a distinct tendinous band on the deep
surface of the muscle; this band does not form a
longitudinal furrow as it does in the dog. The mus-
cle fibers insert into it along its length at a very
oblique angle, so that the biceps is a pennate mus-
cle rather than a parallel-fibered one as in man.
This tendinous band is continued into a short, very
stout, flattened tendon, 12 mm. in width, that
passes between the brachioradialis and pronator
teres to insert into the prominent bicipital tuber-
cle of the radius.
Action: Flexes the forearm.
The biceps is normally, but not invariably, two-
headed in the bears, a degenerate short head usu-
ally arising from the coracoid process with the
brachioradialis (Windle and Parsons, 1897, p. 391).
I have dissected the biceps in a young black bear,
with the following results (fig. 94). The long head
is similar to that of Ailuropoda except that the
small group of accessory fibers coming from the
origin tendon lies along the posterior border of the
muscle, and the tendon of insertion does not begin
far proximad on the deep surface of the muscle.
The short head begins as a slender flattened ten-
don arising from the fascia of the coracobrachialis
just below the head of the humerus. At about the
middle of the humerus the tendon begins to form
a slender muscle belly that lies against the poste-
rior surface of the long head. A few of the most
superficial fibers insert via a lacertus fibrosus into
the fascia over the pronator teres, but most of this
belly inserts with the long head. The biceps was
similar in an adult Tremarctos ornatus dissected by
me. Windle and Parsons found a "very feebly
DAVIS: THE GIANT PANDA
175
M. abd. poll, brevis
Tendo m. ab<i. poll, longus
M. triceps longus
M. triceps medialis
M. pronator teres
Tendo m.y^
flex dig. prof
Tfndo m.flex dig. subl
M. opponeus dig. quinti
. - ^' flex, carpi rad.
Ij ilMJ'W _M. flex. dig. prof.
Olecranon
quinti brevis
M. abd. dig. quinti
M. flex, carpi uln.
Fig. 96. Muscles of the right fore leg of Ailuropoda, medial aspect.
marked" short head in Procyon, and it was also
present in Potos. According to Carlsson (verified
by me) there are two heads in Ailurus.
M. coracobrachialis (fig. 96) is composed of
two heads, a brevis and a longus. The two heads
arise, by a common flattened tendon, from the
coracoid process of the scapula. The short head
arises from the tendon deep to the long head ; the
tendon itself bifurcates and is continued along the
posterior border of each head. The branch of the
musculocutaneous nerve that supplies the biceps
passes between the two heads.
The short head passes around the end of M. sub-
scapularis and inserts into the posterior angle of
the shaft of the humerus immediately proximad of
the tendon of the latissimus dorsi.
The long head runs to the elbow behind the bi-
ceps. Near its insertion it bifurcates, the anterior
fibers inserting on the bony bridge over the ente-
picondylar foramen, while the posterior fibers insert
on the humerus immediately behind the foramen.
The median nerve and branches of the profunda
vein pass between these two parts of the muscle.
Action: Assists the supraspinatus in extending
the arm on the scapula, and helps return the arm
to the intermediate position from either medial or
lateral rotation.
M. brachialis (figs. 88, 95, 96, 133, 134) is com-
posed of two heads, a long head arising along the
deltoid ridge, and a short head arising from the
lateral condylar ridge of the humerus. The two
heads unite to make a common insertion. The
long head is intimately fused with the lateral head
of the triceps proximally, where the two muscles
are attached by a common tendon to the surgical
neck of the humerus immediately behind the del-
toid ridge. From here the origin of the brachialis
continues distad in a U-shaped line, one limb fol-
lowing the deltoid ridge, then the pectoral ridge
below the juncture of these two ridges, to within
50 mm. of the distal end of the shaft; the other
limb extends down the posterior side of the shaft
to the beginning of the lateral epicondylar ridge
at about the middle of the humerus. The short
head arises in a narrow line from the anterior bor-
der of the lateral epicondylar ridge down to within
20 mm. of the distal articulation, then across the
anterior face of the humerus to meet the distal end
of the origin line of the long head.
The two heads make a common insertion. Some
of the fibers insert into the distal two-thirds of a
176
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
tendinous arch that extends from the coronoid
process of the ulna upward (ectad) and forward
(distad) to the intermuscular septum between the
pronator teres and the brachioradialis. The main
insertion is by a stout tendon into the prominent
depression on the anterior surface of the ulna, im-
mediately below the coronoid process.
Innervation: The long head is supplied by the
radial nerve, the short head by the musculocuta-
neous nerve.
Action: Flexes the forearm.
Windle and Parsons (1897, p. 393), in their re-
view of the musculature of the Carnivora, state
that they did not find the short head in any carni-
vore, and that they encountered only radial inner-
vation, although "further observation is necessary
before a definite statement can be made." They
regarded two heads, with radial and musculocuta-
neous innervation, respectively, as the "typical
arrangement" for the Mammalia. Carlsson (1925)
describes a single muscle, with both radial and
musculocutaneous innervation, in Ailurus.
M. epitrochlearis (fig. 88) is an extremely
powerful muscle embracing the whole posterior
part of the upper arm. The internal border is
carried well around onto the medial border of the
arm. The main mass of the muscle arises, by
means of a stout tendinous raphe, from the latis-
simus dorsi. A few of the fibers on the medial
border, representing the medial head of the mus-
cle, arise from a raphe that is fonned with the
ventral fibers of the panniculus carnosus. Inser-
tion is by means of a tendinoxis aponeurosis into
the posterior and medial parts of the olecranon.
Action : Extends the forearm.
M. triceps longus (figs. 88, 95, 96, 133, 134) is
a complex and extremely powerful muscle, com-
posed of incompletely separable lateral and medial
heads. The lateral head is triangular in form, and
proximally shows an incipient division into a super-
ficial posterior part and a slightly deeper anterior
part. It arises, by muscle fibers covered externally
by tendon fibers, from the proximal two-thirds of
the axillary border of the scapula. The medial
head takes a short tendinous origin, deep to that
of the lateral head, from the axillary border of the
scapula near the neck.
The two heads fuse distally, the external fibers
of the lateral head forming a powerful tendon that
receives fibers from the triceps lateralis. Insertion
is into the tip of the olecranon.
M. triceps lateralis (figs. 88, 95, 134) is a pow-
erful prismatic muscle running diagonally across
the external surface of the upper arm and extend-
ing medially behind the humerus. It has a maxi-
mum width (near the humero-ulnar articulation)
of 45 mm.; medially it is continuous with the long
head of the triceps medialis, except near its origin.
The muscle arises chiefly from the surface of the
brachialis lying immediately beneath it. These
two muscles are covered by a heavy common ten-
don layer proximally. The common origin begins
on the surgical neck of the humerus in the area
immediately behind the deltoid ridge, a few of the
fibers coming from the articular capsule. The lat-
eral triceps immediately becomes superficial to the
brachialis, and takes further extensive origin from
the surface of the latter, until the two are sepa-
rated by the brachioradialis. Insertion of the lat-
eral triceps is made chiefly into the posterolateral
border of the olecranon, although the distal part
of the anterior edge of the muscle makes a power-
ful insertion into the fascia of the forearm and
posteriorly there is some insertion into the lateral
head of the triceps longus.
M. triceps medialis (figs. 96, 133, 134) is the
smallest of the three heads of the triceps. It is
composed of two very poorly defined heads, the
posterior of which is separable from the triceps
lateralis only for a short distance after its origin.
The muscle is visible only on the medial surface
of the arm, where the posterior head appears as a
narrow muscle lying between the triceps longus
and the coracobrachialis longus.
The posterior ( long) head arises from a triangu-
lar area on the posterior surface of the neck of the
humerus, the base of the triangle lying against the
lip of the articular surface. The most superficial
fibers arise from the joint capsule. It is independ-
ent of the intermediate head only for about its
proximal third, the main branch of the radial nerve
and branches of the profunda brachialis artery and
vein passing through the interval between them.
Immediately distad of its origin the lateral (deep)
edge of this head fuses with the adjacent edge of
the triceps lateralis, and from this point on, the
two muscles are completely inseparable.
The intermediate head of the triceps medialis
takes an extensive tendinous origin along the pos-
teromedial side of the shaft of the humerus. Its
origin extends from a point above the scar for the
teres major distad almost as far as the end of the
pectoral ridge. This head has little independence
from the other head of the triceps medialis.
Insertion of the fibers coming from the triceps
medialis is made, without intervention of a ten-
don, into the medial and dorsomedial surface of
the olecranon.
Action: The triceps is the chief extensor of the
forearm; it also acts (especially the lateralis) as a
tensor of the forearm fascia.
DAVIS: THE GIANT PANDA
177
M. anconaeus (figs. 95, 134) is a powerful tri-
angular muscle extending more than one-third the
distance up the shaft of the humerus. Medially
it is inseparable from the triceps. It arises from
the well-marked triangular area on the posterior
side of the distal end of the shaft of the humerus,
the origin extending down over the posterior side
of the lateral epicondyle. Insertion is on the pos-
terior side of the olecranon, immediately above the
insertion of the triceps.
Action: Assists the triceps in extending the
forearm.
M. epitrochleo-anconaeus (anconaeus inter-
nus) is not present as an independent muscle. The
most medial fibers of the distal part of the triceps
medialis partly overlie the ulnar nerve and are in-
nervated by a branch of it, however, and appar-
ently represent the epitrochleo-anconaeus. These
fibers insert on the inner side of the olecranon, but
they arise from the shaft of the humerus some dis-
tance above the epicondyle.
C. Muscles of the Forearm
M. palmaris longus (fig. 96) is single. It is
square in cross section, and fusiform when viewed
from the medial side of the forearm. The muscle
takes a very restricted origin from the medial epi-
condyle immediately proximad of the origin of the
humeral part of the flexor carpi ulnaris, from which
its fibers are incompletely separable near the origin.
Near the carpus the muscle separates into a stout
superficial tendon and an entirely separate deeper
fleshy part. The tendon expands into the palmar
aponeurosis, while the fleshy part inserts into the
proximal edge of the transverse fibers of the pal-
mar aponeurosis (see below), which here form a
sheath for the tendon. The fleshy part does not
represent the "palmaris longus internus" of Windle
and Parsons.
Action: Flexes the manus and tenses the palmar
aponeurosis.
The Aponeurosis palmaris (fig. 96) consists
chiefly of fibers that arise from the tendon of the
long palmar muscle and radiate toward the digits.
The fibers extend about equally to all five digits,
lying on the palmar surface as far distad as the
metacarpophalangeal joint. Here the palmar apo-
neurosis gives way to the vaginal ligaments on the
volar surface of the digit, although fibers of the
aponeurosis are continued distad for some distance
along the sides of the digit. A powerful group of
fibers arises from the palmar aponeurosis over meta-
carpal 5 and sweeps transversely across the palm,
to insert on the distal end of the radial sesamoid.
The fasciculi transversi of human anatomy could
not be demonstrated.
Transverse fibers in the antebrachial fascia cor-
responding to the Lig. carpi volare are present
chiefly on the radial side, where they form a wide
band running across the wrist as far as the tendon
of the long palmar muscle.
M. pronator teres (figs. 96, 97, 133) is a flat
muscle lying partly beneath the brachioradialis.
It arises from the anterior side of the proximal end
of the medial epicondyle of the himierus. It is
inseparable from the adjacent border of the flexor
carpi radialis for about half the length of the fore-
arm. The fibers run distad and radial ward, partly
beneath the brachialis. Insertion is made, mostly
beneath the insertion of the brachialis, by means
of a wide aponeurotic tendon into the radial side
of the distal two-thirds of the radius.
Action : Pronates the forearm, turning the palm
upward; flexes the forearm.
M. flexor carpi radialis (figs. 96, 133) is so in-
timately united to the pronator teres at its origin
that the two appear as a single muscle. It arises
from about the center of the anterior side of the
medial epicondyle, its origin being continuous with
that of the pronator teres. The muscle tapers
gradually toward its insertion, becoming tendi-
nous on its ulnar side at about the middle of the
forearm but remaining fleshy down to the carpus
on its radial side. The stout terminal tendon en-
ters the hand through an osteofibrous canal lying
partly beneath the tubercle of the scapholunar,
and inserts into the base of the second metacarpal
(fig. 99; Wood-Jones says the second and third
metacarpals).
Action: Flexes the wrist.
M. flexor carpi ulnaris (figs. 96, 133) consists
of two completely independent parts, which are
separated by the ulnar nerve. The pars ulnaris
is the more superficial, and forms the ulnar con-
tour of the forearm. It arises, chiefly by fleshy
fibers, from the posteromedial part of the olecra-
non. Additional origin is taken medially from the
fascia of the upper arm; and the lateral border,
which is tendinous, is continued with the ante-
brachial fascia for about 70 mm. distad of the
elbow. The fibers converge to a narrow terminal
tendon, which inserts on the proximal side of the
pisiform dorsad of the insertion of the pars humer-
alis. The pars humeralis lies mostly internal to
the pars ulnaris. It arises from the distal side of
the medial epicondyle, where it is inseparable from
the palmaris longus for a short distance, and ter-
minates in a wide, flat tendon that inserts on the
proximal side of the pisiform (fig. 98).
Action: Flexes the wrist and abducts the hand
ulna ward.
178
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
M. flexor digitorum sublimis (figs. 97, 98) is
represented by three small fleshy heads arising from
the volar surface of the flexor digitorum profundus.
Proximally their fibers interdigitate inextricably
with the most superficial head (1) of the profundus.
The sublimis extends only about the distal third
quadratus, so that its proximal end extends onto
the volar surface of the radius. This head lies
deep to the pronator teres and flexor carpi radi-
alis, and most of its fibers insert into the tendinous
part of head L
(4) A narrow, deep head arises from the medial
Mm. luitibrieales
M. brachialis
M. biceps brachii
Tendo m. flex dig. prof.
Tendo m. flex dig. sublimis
Mm. lumbricales
M. flex. dig. prof.
Fig. 97. Deep muscles of right forearm of Ailuropoda, medial view.
of the forearm. Each of the three parts of the
sublimis forms a slender terminal tendon beneath
the transverse carpal ligament. These are distrib-
uted to digits 2, 3, and 4, and are perforated at
the metacarpophalangeal joints by the tendons of
the profundus. Insertion is into the base of the
second phalanx of the digit.
Action : Flexes the middle phalanx on the proxi-
mal phalanx of digits 2-4.
M. flexor digitorum profundus (figs. 97, 98,
133, 134) is very powerfully developed. It is com-
posed of five heads, and terminates in five strong
perforating tendons that are distributed to the
digits. Insertion is into the base of the terminal
phalanx. The structure of the parts of the muscle
is as follows:
(1) The most superficial head arises from the
middle part of the medial epicondyle. It lies along
the ulnar border of the flexor carpi radialis. Most
of the tendon fibers arising from this head are con-
tinued into the tendon of digit 1, but it does not
form a separate tendon as Wood-Jones (1939a)
stated.
(2) A head arises from the lower part of the
medial epicondyle, deep to the origins of the pal-
maris longus and humeral head of the flexor carpi
ulnaris. Distally this head attaches to the under-
lying ulnar head (5), in addition to giving rise to
the three heads of the flexor digitorum sublimis.
(3) A head arises from the proximal two-thirds
of the volar surface of the radius; the medial bor-
der of the origin follows the border of the pronator
border of the condyle of the humerus, just in front
of the epicondyle. Its fibers insert on the ulnar
head (5).
(5) The ulnar head is by far the largest element
of the muscle. It arises from the entire volar sur-
face of the ulna, including the olecranon. The
distal three-fourths of its volar surface is covered
with a heavy tendinous aponeurosis, and it is
chiefly from this aponeurosis that the terminal
tendons of the flexor digitorum profundus arise.
Wood-Jones mentions a deep head arising from
the olecranon ; judging from its position he referred
to the head arising from the condyle (4).
Action: Flexes all the digits, especially the ter-
minal phalanx on the middle phalanx.
M. pronator quadratus (figs. 96, 133) is an
extensive, thick fleshy mass, trapezoidal in outline.
The origin is somewhat narrower than the inser-
tion, and is taken from the distal third of the volar
surface of the ulna. The muscle fans out some-
what to its insertion, which is made into the distal
half of the volar surface of the radius.
Action: Pronates the forearm and hand, turn-
ing the palm upward.
M. brachioradialis (supinator longus of auth-
ors) (figs. 95, 96, 133, 134) is very powerfully de-
veloped, with a width of about 50 mm. on the fore-
arm. It arises by two heads, which are separated
by a branch of the radial nerve. One head arises
from the lateral epicondylar ridge, from a point
60 mm. proximad of the epicondyle up past the
I
DAVIS: THE GIANT PANDA
179
middle of the humeral shaft, some of its fibers be-
ing joined to adjacent parts of the extensor carpi
radialis longus. The other head arises from the
deep surface of the triceps lateralis. The two heads
promptly fuse, and the resulting common mass in-
serts into the prominence on the radial side of the
distal end of the radius.
Action: Flexes the forearm; supinates the fore-
arm and hand, turning the palm downward.
M. extensor carpi radialis longus (figs. 95,
134) arises from the anterior face of the lateral
epicondylar ridge. Its ulnar border is inseparable
from the adjacent border of the extensor carpi
radialis brevis. At about the middle of the fore-
arm the muscle ends in a relatively slender tendon
that passes across the carpus, deep to the extensor
brevis poUicis, to insert into the radial side of the
second metacarpal, just proximad of the center of
the bone.
Action: Extends the hand and abducts it ra-
dial ward.
M. extensor carpi radialis brevis (figs. 95, 134)
IS somewhat more slender than the longus. It is
more or less inseparable from the longus laterally,
and is even more closely united to the extensor
digitorum communis medially, where a tendinous
septum is formed. It arises from the distal part
of the lateral epicondylar ridge. It remains fleshy
somewhat farther distad than the longus, termi-
nating in a tendon that inserts near the base of the
third metacarpal, on the radial side of the bone.
Action: Extends the hand and adducts it ra-
dialward.
M. extensor digitorum communis (figs. 95,
134) is inseparable proximally from the adjacent
muscles on either side. It arises from the distal
part of the lateral epicondylar ridge. The muscle
tapers gradually toward the wrist, becoming very
narrow at the proximal border of the dorsal carpal
ligament. It terminates in four tendons, which go
to the basal phalanges of the second, third, fourth,
and fifth digits.
The tendon going to the second digit comes off
first, about 20 mm. proximad of the others; the
muscle fibers going to this tendon are quite sep-
arate from those going to the other three for most
of the length of the muscle. The tendon to the
third digit comes off independently at the proxi-
mal border of the dorsal carpal ligament. The
tendon to the fourth and fifth digits is common at
first, dividing after ten or twelve millimeters. The
tendons go chiefly to the radial sides of the re-
spective digits.
Action: Extends digits 2-5.
M. extensor digitorum lateralis (BNA: ex-
tensor digiti quinti proprius) (figs. 95, 134) is a
rather slender muscle arising from the middle part
of the lateral epicondyle and from the condyle
itself. At its origin it is more or less inseparable
from the adjacent borders of the extensor carpi
ulnaris and the extensor digitorum communis. Be-
neath the dorsal carpal ligament the muscle forms
two terminal tendons, which go to the ulnar sides
of the basal phalanges of digits 4 and 5.
Action: Assists the common extensor in extend-
ing digits 4-5.
M. extensor carpi ulnaris (figs. 95, 134) arises
by mingled fleshy and tendinous fibers from the
distal end of the lateral epicondyle and from the
condyle. At its origin its fibers are more or less
inseparable from those of the adjacent borders of
the anconeus and extensor digitoi-um lateralis. The
flat insertion tendon, which can be separated from
the dorsal carpal ligament only with difficulty,
attaches to the tubercle on the ulnar side of the
base of the fifth metacarpal.
Action: Extends the hand and abducts it ulna-
ward.
M. supinator (figs. 95, 134) arises from the liga-
ments surrounding the radiohumeral articulation;
there is no origin from the lateral condyle of the
humerus described by Wood-Jones. Insertion is
into the lateral and dorsal surfaces of the radius,
from below the head down to the junction of the
middle and distal thirds. The proximal two-thirds
of the outer surface of the muscle is covered with a
heavy tendinous aponeurosis.
Action: Supinates the forearm and hand, turn-
ing the palm downward.
M. abductor pollicis longus (figs. 95, 96, 98,
134) includes the extensor and long abductor mus-
cles of the thumb in hiunan anatomy. It is a power-
ful muscle arising from the anterior (radial) half of
the dorsal surface of the ulna, from the semilunar
notch to the head ; from the posterior (ulnar) half
of the medial surface of the shaft of the radius,
from the bicipital tubercle to a point just distad
of the center of the shaft; from the interosseous
membrane between these areas; and from the cap-
sule of the elbow joint immediately below the ra-
dial collateral ligament. At the distal end of the
radius the muscle fibers converge to a powerful
compound flat tendon, which passes through the
deep notch on the medial (thumb) side of the head
of the radius, to insert into the proximal end of the
outer surface of the radial sesamoid. The tendon
is divisible throughout its length into two elements,
and the more lateral of these shows a tendency to
subdivide further. There is no attachment to the
180
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Tendo m. flex, carpi rad,
M. flex, carpi rad
Lig. radiocarp. rol.
Tendo m. abductor poll, longus
Lig. carpi trans, (cut)
Os sesamoid, rad.
M. interosseus 1
M. oppwnens pollicis
M. abductor poll, brevis
M. flex. poll, brevis
M. flex, carpi uln.
(pars humeralis)
R. prof, ro/arw . ubi.
Os pisiforme
M. palmaris brevis (cut)
M. abductor dig. quinti
Mm. adductores digitorum
M. interosseus 4
M. opponens dig. quinti
Tendo com. m. flex. dig. prof,
(reflected)
Fig. 98. Deep muscles of palm of Ailuropoda.
pollex, and the "fascial insertion" of the medial
slip between the radial sesamoid and the first meta-
carpal described by Wood-Jones could not be dem-
onstrated.
Action : Abducts the radial sesamoid bone.
In a specimen of Procyon lotor the terminal ten-
don of the abductor longus was separated from the
scapholunar by the radial sesamoid bone, which
was closely bound by fascia to the deep surface of
the tendon. The tendon inserted into the radial
side of the base of metacarpal 1. In a specimen
of Ursiis americanus and one of Tremarctos ornatus
the abductor longus terminated in two tendons
that passed side by side onto the carpus. The
larger of these had the normal insertion into the
base of metacarpal 1, whereas the smaller inserted
into the radial sesamoid.
M. extensor indicus proprius (figs. 95, 134)
is a thin and rather slender muscle arising from
the middle third of the doi^sal border of the ulna
and extensively from the underlying surface of the
abductor pollicis longus. Just before reaching the
base of the carpus the muscle forms two terminal
tendons, which pass diagonally across the carpus
and metacarpus to insert into the base of the first
phalanges of digits 1 and 2. The tendon to digit 2
is considerably the larger, and fibrous bands are
carried across from it to digit 1.
Action : Assists the common extensor in extend-
ing digits 1-2.
D. Muscles of the Hand
M. palmaris brevis (figs. 96, 98) does not seem
to have been described hitherto in a carnivore. In
Ailuropoda a small group of muscle fibers arising
from the anterior face of the pisiform and inserting
partly into the palmar aponeurosis and partly into
the skin in front of the outer carpal pad can only
DAVIS: THE GIANT PANDA
181
represent this muscle. The fibers going to the
palmar aponeurosis extend part way across the
flexor digiti quinti brevis, while those going to the
skin arch laterad. Innervation is by a twig from
the palmar division of the deep branch of the ulnar
nerve, and the blood supply is by a short twig from
the branch of the mediana propria that supplies
the outer side of digit 5.
Action: Helps to cup the palm of the hand.
M. abductor pollicis brevis (fig. 98) is incom-
pletely separable from the opponens and short
flexor. It is represented by a group of fibers ly-
ing at the distal border of the interspace between
the radial sesamoid and the pollex. Origin is from
the inner face of the radial sesamoid, and insertion
into the radial side of the base of the first phalanx
of the pollex.
Action : Adducts the radial sesamoid bone.
M. flexor pollicis brevis (fig. 98) is a slender
muscle incompletely separable from the abductor
pollicis brevis. Origin is from the transverse car-
pal ligament and the scapholunar near the base
of the first metacarpal. The muscle inserts into
the radial side of the base of the pollex, close to the
insertion of the abductor.
Action: Flexes and abducts the pollex.
M. opponens pollicis (fig. 98) is a large muscle
occupying most of the interspace between the ra-
dial sesamoid and the pollex. It arises extensively
from the inner face of the radial sesamoid, and in-
serts with the short abductor into the radial side
of the first phalanx of the pollex.
Action: Adducts the radial sesamoid bone.
In a specimen of Procyon lotor the short muscles
of the pollex were represented by a superficial and
a deep element, which arose from the transverse
carpal ligament and the scapholunar (no relation
with the radial sesamoid), and inserted into the
radial side of the base of the first phalanx. In a
specimen of Ursus americanus and one of Tre-
marctos ornatus these short muscles of the pollex
were represented by a single muscle mass, which
arose extensively from the radial sesamoid in addi-
tion to the origin from the carpal ligament and
scapholunar.
M. abductor digiti quinti (figs. 96, 98) is a
large muscle arising extensively from the anterior
and dorsal surfaces of the pisiform. The fibers
converge to a tendon that inserts partly into the
underlying surface of the opponens digiti quinti,
and partly continues on to the ulnar side of the
base of the first phalanx of digit 5.
Action: Abducts and flexes the fifth digit.
M. flexor digiti quinti brevis (figs. 96, 133) is
composed of two heads, one deep to the other, that
insert by a common tendon. The superficial head
arises exclusively from the connective tissue pad
over the pisiform, whereas the deep head arises
partly from the inner border of the pisiform and
partly from the superficial layer of the transverse
carpal ligament. The common tendon gives off a
slip to the base of the first phalanx of digit 5, but
most of its substance is continued to the base of
the second phalanx.
Action : Flexes the proximal phalanges of digit 5.
M. opponens digiti quinti (figs. 96, 98) is a
powerful fleshy muscle arising by two heads. One
head takes origin from the tip of the unciform and
the adjoining part of the deep layer of the carpal
ligament. The other head arises from the anterior
surface of the pisiform, deep to the origin of the
abductor. Insertion, as Wood-Jones pointed out,
is into the sesamoid on the ulnar side of the meta-
carpophalangeal joint of digit 5.
Action: Flexes and adducts the fifth metacarpal.
Mm, lumbricales (fig. 97) occupy the usual
position between the tendons of the flexor digi-
torum profundus. Origin is from the wide com-
mon tendon of the flexor digitorum profundus,
from which four bellies radiate into the interten-
dinous spaces. Insertions are made by means of
flat tendons into the radial sides of the bases of the
second phalanges of digits 2 to 5.
Action: Flex the basal phalanges of digits 2-5
and draw them toward the thumb.
Mm. adductores digitorum (superficial pal-
mar muscles, Wood-Jones) (fig. 98). The most
superficial layer of palmar muscles cannot be ho-
mologized with the interossei of human anatomy;
the belly going to the thumb represents the ad-
ductor pollicis of man. Three bellies arise together
from the transverse carpal ligament and the fascia
covering the underlying carpal bones. The largest
belly goes to the radial side of the base of the first
phalanx of the fifth digit. Another belly goes to
the ulnar side of the first phalanx of the pollex.
The middle, and by far the smallest, belly goes to
the ulnar side of the second digit. Wood-Jones
described a fourth very slender belly to the third
digit; this slip was absent in our specimen.
Action: Flex the digits; draw digits 1 and 5
toward the midline of the hand.
In a specimen of Ursus americanus the arrange-
ment of these muscles was identical with our speci-
men of Ailuropoda.
Mm. interossei (fig. 99) are composed of four
groups of muscles, made up of ten separate slips.
The first group arises from the base of the first
182
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
metacarpal, and is made up of two slips: these go
to the ulnar side of the pollex and the radial side
of digit 2, respectively. The second gi'oup arises
from the third metacarpal, and is made up of three
any importance to its absence in the panda. Ailu-
ropoda differs from the bears, and apparently from
all other carnivores, in the distinctness of the two
heads of the brachialis.
Os scapJwlunare Os magnum
O.s trapezoid \ I Os unciforme
Os cuneijorme
Tendo m. flex, carpi rad.
Os trapezium
Lig. carpi trans, {cut)-^^
Os sesamoid, rad.
M. interosseus 1
Os pisiforme
Lig. carpi trans, (cut)
M. interosseus 4
M. opponens dig. quinti
Fig. 99. Interosseous muscles of manus of Ailuropoda.
slips; two of these go to either side of digit 2, while
the third, which is very slender, goes to the radial
side of digit 3. The third group arises from the
fourth metacarpal, and is made up of three heads ;
two of these go to either side of digit 3, the third
going to the ulnar side of digit 4 ; a few of the fibers
are also contributed to the ulnar side of digit 4.
The fourth group arises from the fifth metacarpal,
and is made up of two heads; one goes to the ulnar
side of digit 4, the other to the radial side of digit 5.
Action : Flex the phalanges on the metacarpals.
M. flexor brevis digitorum manus is absent.
This muscle is also absent in bears, but is present
in all procyonids. It inserts into the vaginal sheath
of digit 5.
E. Review of Muscles of the Fore Limb
In general the muscles of the fore limb in Ailu-
ropoda agree closely with those in Ursus. Often
correspondence extends down to minor details of
muscle structure and attachment sites. In the
tabulation of myological characters (p. 197) the
panda and the bears disagree in only one point:
the short head of the biceps, usually present in
Ursus, is absent in Ailuropoda. Since this head
is known to be variable in Ursus, I do not attach
There is a generalized increase in the mass of the
musculature in the anterior part of the body, par-
ticularly in the neck, shoulder, and upper arm.
This is evident in a direct comparison of individual
muscles with those of Ursus and in the heavy sur-
face modeling on the scapula and humerus, and it
is indicated in the relative weights of the muscula-
ture of the fore and hind limbs (Table 15, p. 195).
I can find no functional reason for this heavy mus-
culature. This is the region of the body closest
to the head, and furthermore there is a gradient
away from the head: the neck and shoulder mus-
culature is most affected, the upper arm less so,
and the lower arm and hand least. This strongly
suggests a generalized regional effect, centered in
the head and decreasing in a gradient away from
the head, similar to that seen in the skeleton.
The most distinctive feature of the fore limb in
Ailuropoda is the enlarged and mobile radial sesa-
moid bone. The muscles associated with this bone
in the panda are the palmaris longus, the opponens
pollicis, and the abductor pollicis longus and brevis.
Normally in carnivores these muscles insert into
the base of the thumb, and the radial sesamoid is
a typical sesamoid bone developed in the tendon
of the long abductor where it glides over the scapho- j
lunar. In bears, however, the radial sesamoid isj
DAVIS: THE GIANT PANDA
183
Table 14. RELATIVE WEIGHTS OF MUSCLES OF THE SHOULDER AND ARM IN CARNIVORES
Ailuropoda'
Wt. in
gms. %
Supraspinatus 122
Infraspinatus 1 19
Acromiodelt. +Spinodelt 85
Teres major 72
Subscapularis +Teres minor 168
Biceps 75
Coracobrachialis 16
Brachialis 52
Epitrochlearis 58
Triceps longus 189
Triceps lateralis 95
Triceps medius 55
Anconaeus 26
10.8
10.5
7.5
6.4
14.8
6.6
1.4
4.6
37.4
Totals 1132 100.0
* Half-grown individual (Su Lin).
** Data from Haughton.
Tremarctos
Wt. in
gms. %
136
104
108
60
188
110
25
74
56
237
135
57
19
10.4
7.9
8.3
4.6
14.4
8.4
1.9
5.7
38.6
1309 100.2
Ursus
Cants
amerieanus** familiaris*
% %
9
9,
8,
4,
14,
8.
1.
5.
38.3
99.9
15.4
11.0
5.7
4.8
9.4
4.8
.5
2.8
45.7
100.1
Leo Uo**
%
12.9
11.6
4
8
13
7
38.7
99.9
enlarged and the basic panda condition of the mus-
cles already exists: the terminal tendon of the long
abductor ends partly in the radial sesamoid (p. 179),
and the short muscles (brevis and opponens) at-
tach extensively to the radial sesamoid. In other
words, all elements attaching to the radial sesa-
moid in Ailuropoda already have some attachment
to this bone in Ursus, apparently simply as a me-
chanical result of the enlargement of the sesamoid
in bears. The step from the bear condition to the
panda condition involves only a further shift of
muscle attachments in favor of the sesamoid, and
such a shift would probably result automatically
from the further enlargement of the sesamoid bone:
the size of the bone simply blocks off the tendon of
the long abductor from the poUex, and the short
muscles from their original attachment sites on the
transverse carpal ligament and the scapholunar.
Thus, the musculature for operating this remark-
able new mechanism functionally a new digit- re-
quired no intrinsic change from conditions already
present in the panda's closest relatives, the bears.
Furthermore, it appears that the whole sequence
of events in the musculature follows automatically
from simple hypertrophy of the sesamoid bone.
Other subtle differences in the musculature, im-
portant from the functional standpoint, are revealed
by comparing the relative masses of individual
muscles. Such data are available for the shoul-
der and arm in a series of carnivores (Table 14).
These figures reveal that in the panda and the
bears the medial rotator of the arm (subscapu-
laris), the abductor of the arm (deltoid), and the
flexors of the elbow (biceps, brachialis) are rela-
tively large, whereas in the dog (the horse is very
similar) the extensors (supraspinatus, triceps) are
dominant. The lion tends to be intermediate be-
tween the panda-bear condition and the dog-horse
condition. These muscle-mass relations are obvi-
ously correlated with the differing mechanical re-
quirements in a limb used for ambulatory walking
and prehension versus one used for cursorial run-
ning. The morphogenetic mechanisms through
which such anatomical differences are expressed,
and thus the basis on which natural selection could
operate, are unknown. Indeed, in view of Fuld's
data on bipedal dogs (p. 148), it is not even
certain that differences in muscle-mass relations
among related forms are intrinsic to the muscu-
lature.
IV. MUSCLES OF THE HIND LEG
A. Muscles of the Hip
1. Iliopsoas Group
M. psoas major (fig. 100) lies ventrad of the
medial part of the quadratus lumborum. It arises,
by successive digitations, from the bodies and
transverse processes of all the lumbar vertebrae.
Each slip has a double origin: medial fibers arise
from the side of the body of the vertebra, and lat-
eral fibers from the transverse process; a part of
the quadratus lumborum is embraced between.
The muscle is joined posteriorly by the iliacus,
and inserts by a wide common tendon with it into
the lesser trochanter.
M. iliacus (fig. 100) is a small muscle arising
from the ventral face of the ilium. It is more or
less inseparable from the psoas major medially,
and inserts by a common tendon with it into the
anterior border of the lesser trochanter. The fibers
of the iliacus insert into the ventral part of the
tendon.
184
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
M. quadratus lumborum
M. iliocostalis
M. psoas minor.
M. psoas major.
M. iliacus
M. iliopsoas
M. obturator extemus
M. quadratus femoris
Fig. 100. Deep muscles of back and hip of Ailuropoda, ventral view.
M. psoas minor (fig. 100) lies deep to (ventrad
of) the psoas major, from which it is entirely free.
It arises from the bodies of the last thoracic and
first three lumbar vertebrae, and inserts by a stout
flat tendon into the ilium just above the iliopec-
tineal eminence.
Action: The iliopsoas flexes the thigh and ro-
tates the femur laterally. When the thigh is fixed,
it flexes the pelvis on the thigh.
2. Gluteal Group
The gluteal muscles arise chiefly from the ilium,
and in Ailuropoda they have been affected by the
DAVIS: THE GIANT PANDA
185
reduction in the area of the wing of the ilium. This
reduction in attachment area is not reflected in
their mass, which is relatively greater than in any
other carnivore examined. As often happens when
the area available for muscle attachment is re-
stricted, the muscles of the gluteal group tend to
fuse and to extend their areas of origin to fascia.
The insertions of these muscles do not differ much
from those of Ursus.
M. glutaeus superficialis (figs. 88, 138) is a
broad, thin, fan-shaped sheet completely covering
the middle and deep gluteals. It arises, by a wide
aponeurosis tightly adherent to the underlying
fascia of the middle gluteal, from the iliac crest,
the lumbodorsal fascia over the last lumbar ver-
tebra, the entire sacral fascia, the fascia over the
first caudal, and, by fleshy fibers, from the ante-
rior border of the ischial tuberosity directly above
the attachment of the sacrotuberous ligament. It
has no attachment to the transverse processes of
the sacrals or caudals, or to the sacrotuberous liga-
ment. In addition, the anteriormost fibers are
reflected around the anterior border of the middle
gluteal onto the deep surface of the middle gluteal,
to insert with these middle gluteal fibers into the
fascia covering the dorsal surface of the iliopsoas.
Anteriorly the superficial gluteal borders on the
sartorius and tensor fasciae latae, posteriorly on
the semimembranosus and biceps. It is not com-
pletely separable from the tensor. Its fibers con-
verge rapidly to a stout tendon, which inserts into
the prominent scar below the great trochanter.
There is a large gluteofemoral bursa beneath the
muscle at its insertion.
Action : Flexes the thigh and rotates the femur
medially.
M. glutaeus medius (figs. 88, 138) is the most
powerful element of the gluteal complex, although
it exceeds the mass of the superficial gluteal much
less than in other carnivores. It consists of a sin-
gle heavy fan-shaped layer, 85 mm. wide, com-
pletely hidden beneath the superficial gluteal. It
is not completely separable from the underlying
deep gluteal. Anterior to the greater sciatic notch,
origin is from the lumbodorsal fascia and from the
gluteal surface of the ilium; posterior to the notch,
origin is from the lateral edge of the crest formed
by the fused transverse processes of the sacral ver-
tebrae. Insertion is by mingled muscle and tendon
fibers into the dorsal and anterior borders of the
great trochanter.
Action: Extends and abducts the thigh.
M. glutaeus profundus (fig. 138) is the small-
est of the gluteal muscles. It lies entirely beneath
the middle gluteal, from which it is separated by a
large trunk of the superior gluteal nerve; its bor-
ders conform rather closely to those of the medius.
The profundus consists of a single wide layer,
somewhat thinner than the medius. Origin is from
almost the entire inferior gluteal line, beginning a
short distance behind the anterior superior iliac
spine and continuing posteriorly onto the body of
the ilium in front of the acetabulum. Insertion is
by a wide tendon into the anterior border of the
great trochanter, deep to the insertion of the mid-
dle gluteal.
Action: Abducts the thigh and rotates the fe-
mur medially.
M. tensor fasciae latae (figs. 88, 137, 138) is
not completely separable from the adjacent bor-
der of the superficial gluteal. It arises from the
lateroventral edge of the ilium, along a line run-
ning caudad from the crest. It inserts into the
fascia lata in a curved line, convex distally, that
begins at the prominence for the insertion of the
superficial gluteal and ends at about the middle
of the thigh.
Action: Tenses the fascia lata and assists the
superficial gluteal in flexing the thigh and rotating
it medially.
3. Obturator Group
M. gemellus anterior (figs. 88, 138) is com-
pletely free from the obturator internus. It is a
small muscle arising from the ischium along the
lesser sciatic notch anterior to the ischial spine.
The fibers converge to insert into the anterior part
of the internal obturator tendon for a distance of
20 mm.
M. piriformis (figs. 88, 138) is completely dis-
tinct from the middle gluteal, its anterior third
being overlapped by the posterior part of the mid-
dle gluteal. Origin is from the antero-inferior bor-
der of the sciatic notch (as in Ursu^) and from the
lateral edge of the fused transverse processes of
the sacral vertebrae. Insertion is made by min-
gled muscle and tendon fibers into the dorsal (prox-
imal) border of the great trochanter, deep to the
insertion of the middle gluteal.
Action: Abducts the femur.
M. obturator internus (fig. 138) is much
smaller than the external obturator, as in the
Ursidae. It has the usual origin from the pelvic
surfaces of the pubis and ischium where they form
the margin of the obturator foramen. The fibers
converge to a long flat tendon that passes out over
the lesser sciatic notch, to insert into the trochan-
teric fossa of the femur. There is a large mucous
bursa beneath the obturator tendon where it passes
over the ischium.
186
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Action: Abducts the femur and rotates it lat-
erally.
M. gemellus posterior (fig. 138) is larger than
the anterior gemellus, and, like it, is free from the
internal obturator. It arises from the ischium im-
mediately in front of the tuberosity and beneath
the sacrotuberous ligament. Insertion is narrow
and by means of tendon fibers, into the posterior
edge of the tendon of the internal obturator. In-
sertion of the posterior gemellus is distad of the
insertion of the anterior gemellus.
Action: Abducts the femur and rotates it lat-
erally.
M. quadratus femoris (figs. 88, 100, 138) is a
stout quadrilateral muscle arising from the dorsal
third of the lateral surface of the ramus of the
ischium, directly below the ischial tuberosity. In-
sertion is by means of a short tendinous aponeu-
rosis into the crescentic inter-trochanteric line.
Action: Extends the thigh and rotates the fe-
mur laterally.
M. obturator externus (figs. 100, 138) is of
the usual triangular form. It arises from the lat-
eral surface of the ascending ramus of the pubis,
from the pubis and ischium along the symphysis,
from the descending ramus of the ischium caudad
of the obturator foramen, and from the external
surface of the obturator membrane. The fibers
converge strongly to a powerful tendon, which is
inserted into the proximal part of the trochanteric
fossa.
Action : A powerful lateral rotator of the thigh
and a weak extensor and adductor.
B. Muscles of the Thigh
M. semimembranosus (figs. 88, 89, 137, 138,
140) is divided, as in other carnivores, into two
subequal parts: an anterior belly that inserts into
the femur, and a posterior belly that inserts into
the tibia. These arise together from the postero-
lateral surface of the descending ramus of the
ischiimi immediately below the origin of the bi-
ceps and semitendinosus. They promptly divide
and run distad, diverging slightly in their course.
The anterior belly lies at first mostly mesad of
the posterior belly. It inserts, by fleshy fibers,
chiefiy into the medial epicondyle of the femur
just anterior to the origin of the medial head of
the gastrocnemius. The line of origin continues
distad onto the tibial collateral ligament. The
posterior belly inserts, by mingled fleshy and ten-
don fibers, into the infraglenoid margin of the
median condyle of the tibia.
Action: (1) extends the thigh; (2) flexes the leg.
M. semitendinosus (figs. 88, 89, 138) arises
from the ischial tuberosity only; there is no extra
head from the caudal vertebrae. Origin is by short
tendon fibers, above and partly behind the origin
of the biceps. Insertion is made for the most part
by a short flat tendon, 50 mm. in width, into the
anterior crest of the tibia, beneath the insertion of
the sartorius. The posterior fibers are continued
distad into the fascia of the lower leg.
Action: (1) extends the thigh; (2) flexes the leg.
M. sartorius (figs. 88, 89, 137, 139) is a single
fiat band lying superficially on the median and an-
terior sides of the thigh. It arises, by mixed fieshy
and tendon fibers that are continuous with those
of the middle gluteal dorsally, from the anterior
superior iliac spine and the inguinal ligament. In-
sertion is made in a long sinuous line running along
the medial border of the patella, across the liga-
ments of the knee joint, and down along the me-
dial side of the anterior crest of the tibia for about
half its length.
Action: (1) flexes the thigh; (2) flexes the leg.
M. rectus femoris (figs. 88, 89, 103, 137) is a
fusiform muscle wedged in between the vastus lat-
eralis and vastus medialis; it is intimately associ-
ated with both these muscles distally. The rectus
arises by two short stout tendons that attach close
together, one above the other, to a prominent
roughened scar on the anterior lip of the acetab-
ulum. Almost the entire deep surface of the mus-
cle is covered with a glistening tendinous aponeu-
rosis, but this does not form a terminal tendon.
Insertion is into the proximal border of the patella,
partly by fleshy fibers and partly by fibers of the
tendinous aponeurosis.
Action : Extends the leg and flexes the thigh.
M. vastus lateralis (figs. 88, 102, 103, 138-140)
is, as usual, the largest component of the quadri-
ceps extensor group. It is completely inseparable
from the vastus intermedius throughout its entire
length. Origin is from the posterolateral surface
of the great trochanter and the shaft of the femur
in a narrow line along the lateral lip of the linea
aspera nearly down to the lateral epicondyle. At
its distal end it fuses with the rectus femoris and
inserts in connection with it into the dorsal and
lateral borders of the patella.
Action: Extends the leg, assisted by the other
muscles of the quadriceps femoris.
M. pectineus (figs. 89, 137) is a wedge-shaped
muscle lying between the adductor and the vastus
medialis. It may with difficulty be separated into
two layers: an anterior ("superficial") and a pos-
terior ("deep"). It is easily separable from the
adductor except at its insertion. Origin is by a
DAVIS: THE GIANT PANDA
187
thin flat tendon from the crest on the anterior
border of the ascending ramus of the pubis, from
the iHopectineal eminence nearly to the symphy-
sis. The tendon of origin is intimately united, on
its superficial surface, with the prepubic tendon
(p. 166). Insertion is by a flat tendon, which be-
comes increasingly heavy distally, into the middle
third of the medial lip of the linea aspera. The
insertion line terminates inferiorly at the level
where it meets the femoral vessels emerging from
the hiatus adductorius. The anterior layer is in-
nervated by N. femoralis, the posterior by N. ob-
turatorius.
Action: Adducts and flexes the thigh and ro-
tates the femur laterally.
M. gracilis (figs. 89, 137) arises by mingled ten-
don and fleshy fibers from the entire length of the
short symphysis and for some distance up the an-
terior border of the descending ramus of the pubis
anteriorly, and about half way up the posterior
edge of the descending ramus of the ischium pos-
teriorly. It is a flat muscle about 70 mm. in width,
covering the posteromedial surface of the thigh.
It inserts by means of a short tendinous aponeu-
rosis into the medial side of the proximal end of the
tibia, immediately behind the insertion of the sar-
torius. The posterior fibers are continued distad
into the fascia of the lower leg.
Action: (1) adducts the thigh; (2) flexes the leg.
M. adductor (figs. 88, 89, 102, 137, 138) can-
not be separated with any certainty into a magnus,
longus, and brevis. As in Ursus (original obser-
vation), it is composed of a continuous sheet that
is reflected back on itself at its distal (posterior)
edge to form a double-layered muscle with a deep
pocket separating the two layers; the pocket is
open proximally and posteriorly. This is strikingly
similar to the structure of the pectoralis major of
man as described by Zuckerkandl (1910).
The anterior layer of the adductor arises in a
long narrow U-shaped line that descends along the
ventral half of the external surface of the acetab-
ular ramus of the pubis, crosses the entire length
of the symphysis pelvis, and ascends nearly half
way up the descending ramus of the ischium. The
posterior layer arises from a relatively small area
on the external face of the descending ramus of
the ischium, deep to the anterior layer and directly
adjoining the area of origin of the external obtu-
rator. The anterior layer of the adductor is very
wide and thin at its origin, the posterior layer nar-
row and relatively thick.
The two layers insert side by side into the linea
aspera (which is very poorly defined in Ailuropoda
and the bears), on the posterolateral side of the
shaft of the femur. Insertion begins proximally
just below the level of the third trochanter. The
posterior layer is intimately associated with the
pectineus at its insertion. Distally, at the distal
sixth of the shaft of the femur, both layers leave
an opening, the hiatus adductorius, for the passage
of the femoral vessels. Distad of the hiatus, inser-
tion is by muscle fibers into the medial side of the
posterior surface of the femur, including the medial
epicondyle and the adjacent popliteal surface.
Action: Adducts and extends the thigh.
M. biceps femoris (figs. 88, 138) is completely
differentiated from the glutaeus superficialis and
tensor fasciae latae. It is composed of a single
head; the small posterior head, which is partly dif-
ferentiated in Ursus and completely separate prox-.
imally in Canis, is indistinguishable in Ailuropoda.
The muscle arises, by a short stout tendon, from
the lateral part of the ischial tuberosity; no fibers
come from the caudal vertebrae or the sacrotuber-
ous ligament. The muscle expands rapidly into a
fan-shaped sheet, reaching a width of 185 mm. at
its distal end. Near its insertion the muscle ter-
minates abruptly in a continuous wide aponeuro-
sis that passes into the fascia lata proximally and
the crural fascia below the knee. Insertion is thus
indirectly into the lateral side of the patella, the
patellar ligament, and the anterior crest of the
tibia. The most distal part of the aponeurotic
sheet turns abruptly distad and caudad to the
tuber calcis. Insertion of the biceps thus extends
from immediately above the knee to the heel, the
most distal extension of the biceps insertion known
to me for any carnivore.
Action: The muscle is chiefly a flexor of the leg;
the anteriormost fibers extend the thigh.
M. abductor cruris posterior (abductor cruris
caudalis; Ziegler, 1931; Baum and Zietzschmann,
1936). This muscle was present on the left limb
only, as a narrow, rope-like tract of fibers. Origin
was from the ischial tuberosity immediately be-
neath the biceps, wedged in between the biceps
and the quadratus femoris. The muscle ran distad
deep to the biceps and inserted into the posterior
surface of the femur a few millimeters above the
condyles. Innervation was by a branch of the
sciatic nerve.
This muscle is well known in the dog, where it
forms a ribbon-like band arising from the sacro-
tuberous ligament and inserting into the crural
fascia. It is described by Shepherd (1883) for Ur-
sus americanus under the name "lesser portion of
the adductor," and by Carlsson (1925) for Ursus
arctos under the name "caudo-femoralis,"' as aris-
' Carlsson's "femoro-coccygeus" is the caudofemoralis of
Windle and Parsons and the abductor cruris cranialis of
Ziegler.
188
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
ing from the ischial tuberosity and inserting into
the distal part of the femur, as here described for
Ailuropoda. The muscle is unknown from other
carnivores.
M. tenuissimus (fig. 88) arises from the fascia
over the posterior border of the gluteus superfici-
ahs, immediately anterior to the origin of the bi-
ceps femoris. The muscle, which is a narrow
ribbon only about 12 mm. wide throughout most
of its length, lies wholly beneath the posterior bor-
der of the biceps femoris. At the distal end of the
biceps the tenuissimus is continued into the same
fascia as that by which the biceps inserts.
Action: Assists the biceps in flexing the leg.
M. vastus intermedius lies beneath the vastus
lateralis, and the two muscles are inseparable. Ex-
tensive origin is taken from the shaft of the femur
between the origins of the vastus lateralis and the
vastus medialis, from the greater trochanter distad
nearly to the patellar surface. Insertion is into
the capsule of the knee joint.
M. vastus medialis (figs. 89, 139) is triangular
in cross section. It arises by a heavy aponeurosis
along nearly the entire length of the posteromedial
border of the femur. Origin begins on the neck
just below the articular capsule and extends along
the linea aspera to within a few millimeters of the
medial epicondyle. Insertion is into the proximal
and medial borders of the patella.
Action : Assists the other quadriceps muscles in
extending the leg.
C. Muscles of the Leg
M. gastrocnemius (figs. 101, 138, 140) consists
of the usual lateral and medial heads, the edge of
the plantaris appearing on the surface between
them. The medial head is slightly smaller than
the lateral. It arises, by mingled tendon and fleshy
fibers, from the medial condyle of the femur. At
the junction of the middle and lower thirds of the
leg it forms a flat tendon that joins the tendon of
the lateral head. The lateral head is fused insep-
arably with the plantaris proximally, although a
cross section of the two muscles shows a fibrous
septum between them; distally, where the gastro-
cnemius becomes tendinous, they are easily sep-
arable. The common origin of the two muscles is
from the lateral condyle of the femur. The termi-
nal tendon of the lateral head of the gastrocnemius
is smaller than that of the medial head. The two
unite and insert into the outer side of the calca-
neus. There is no sesamoid in the origin of either
head.
Action: Extends the foot; flexes the knee.
M. plantaris (fig. 101) is inseparable from the
lateral head of the gastrocnemius proximally, and
arises with it from the lateral condyle of the femur
(fig. 102). It forms a stout tendon distally, which
twists around that of the gastrocnemius so that it
comes to lie externally, and spreads out over the
calcaneus. The aponeurosis-like tendon, which
attaches to the distal end of the calcaneus on either
side, is continuous with the plantar aponeurosis.
Action : Assists the gastrocnemius in extending
the foot and flexing the knee.
M. soleus (figs. 101, 140) is enormously devel-
oped, greatly exceeding the combined heads of the
gastrocnemius in size. It is a flattened fusiform
muscle, 57 mm. in greatest width. Origin is by
fleshy fibers from the posterior side of the head of
the fibula and the lateral condyle of the tibia, from
the distal end of the fibular collateral ligament,
and extensively from the intermuscular septum
between it and the peroneus brevis. Insertion is
into the calcaneus, with considerable attachment
also to the deep surface of the common tendon
formed by the plantaris and the lateral head of the
gastrocnemius.
Action: Extends the foot.
M. popliteus (figs. 102, 140) is an extensive
and rather heavy triangular sheet arising by a
powerful flat tendon from the outer side of the
lateral condyle of the femur. Insertion is into a
long triangular area mesad of the popliteal line on
the posteromedial surface of the tibia, for its proxi-
mal two thirds.
Action: Flexes the leg and rotates it medially.
M. flexor digitorum longus (flgs. 102, 140)
arises almost entirely from the underlying surface
of the tibialis posterior; its origin reaches the tibia
only behind and below the lateral condyle, where
a few of the fibers gain a tendinous attachment.
The exposed posterior surfaces of the flexor digi-
torum longus and the tibialis posterior are covered
by a common continuous layer of tendinous fascia
where they lie beneath the popliteus. The tendon
of the flexor digitorum longus, which is smaller
than that of either the flexor hallucis longus or the
tibialis posterior, lies in a groove behind the me-
dial malleolus in company with the tendon of the
tibialis posterior. It joins that of the flexor hallu-
cis longus from the medial and deep sides to form
the conjoined tendon.
Action: Flexes the phalanges of all the toes.
M. flexor hallucis longus (figs. 102, 140) is the
largest of the deep flexor muscles, as is usual in
carnivores. Origin is from the posterior surface of
the shaft of the fibula throughout nearly its entire
length, from the interosseous membrane between
Lig. coll. fibulare
M. plantaris
M. gastrocnemius (cap. lat.).
M. soleus
Tendo m. gastrocnemius (cap. med.V
Tendo m. plantaris
Tendo m. biceps femoris icut)
Lig. trans, cruris
Tuber calcanei
Lig. cruciatum crurii
M. abductor dig. quinti
Aponeurosis platitar is icul)
M. flex. dig. quinli brevis
M. tibialis ant.
.M. ext. dig. longua
M. peronaeus Jongui
M. peronaem tertius
M. peronaeus brevia
Tendo m. peronaei tertii
M. ext. dig. brevis
Fig. 101. Muscles of the right leg of Ailuropoda, lateral view.
189
M. ftddoctor magnus.
M. gastTocDcmini (cap. iiied.\
M. semimemfaraQosQS,
M. flex, haltucis brevis
Lin. ^- Jtbuian
M. \-astus lateralis
gastroc (cap. iat.)
M. flex, balhins kwgas
M. peronaevE tolitB
M. perooaeiK brevis
Tuber cakaei
.Tendo peronaeus kngiB
Aportemnsis plamtariM (otf)
M. ^xiuctcr dig. quinti
M. Hex. dip. bmis
Accessor>- slips of flex. d;g. brevis
M. flex. dig. quinti brevis
Mm. lumbrica^es
flex dig. longus
Fig. 102. Muscles of the right leg of AUuropodOt posterior view.
190
DAVIS: THE GIANT PANDA
191
the fibula and tibia, from the adjacent lateral sur-
face of the tibia, and from the septum between the
muscle itself and the peroneal muscles. Proxi-
mally a very definite group of fibers arises from
the fibular collateral ligament. The muscle is bi-
pennate, the tendon beginning at the juncture of
the proximal and middle thirds. The tendon,
which is very powerful, is joined by that of the
flexor digitorum longus. The resulting conjoined
tendon breaks up at the proximal end of the meta-
tarsals into five slips, which are distributed to the
digits. Each perforates the tendon of the flexor
digitorum brevis at the metatarsophalangeal joint,
and inserts into the terminal phalanx.
Action: Flexes the phalanges of all the toes.
M. tibialis posterior (fig. 102) is hidden be-
neath the popliteus proximally, and partly beneath
the flexor digitorum longus distally. Origin, from
the posterior surface of the shaft of the tibia lat-
eral to the popliteal line, extends nearly the entire
length of the shaft. The stout terminal tendon,
after passing through the malleolar groove behind
the medial malleolus, passes across the neck of the
astragalus to its insertion on the tibial sesamoid.
Action: Inverts and extends the foot.
M. tibialis anterior (figs. 101, 103, 139) is in-
completely separable into two parts; this is true
even of the proximal part of the terminal tendon.
The separation involves only the superficial fibers,
the deeper fibers refusing to separate. Origin is
from the anterior surface of the lateral condyle of
the tibia and the proximal third of the lateral sur-
face of the shaft of the tibia, with a delicate origin
from the proximal half of the fibula. At the distal
end of the tibia the muscle forms a powerful flat
tendon, which inserts into the outer side of the
base of the first metatarsal.
Action : Inverts and flexes the foot.
M. extensor digitorum longus (figs. 101, 103,
139) arises by a long narrow tendon from a pit on
the external condyle of the femur. The muscle
expands gradually as it passes distad, reaching a
maximum over the distal end of the tibia. The
muscle becomes tendinous at the tarsus. The four
terminal tendons go to the phalanges of digits 2-5;
that to digit 2 is extremely slender and arises as a
slip from the tendon to digit 3.
Action: Flexes the ankle joint; extends the four
lateral toes, with eversion of the foot.
M. extensor hallucis longus (figs. 103, 139) is
a rather slender muscle arising from the distal half
of the medial surface of the fibula; it forms a raphe
with the peroneus brevis throughout the length of
of its origin. The terminal tendon, which compares
with those of the extensor digitorum longus in size,
inserts into the terminal phalanx of the hallux,
with considerable fibrous attachment to the basal
phalanx. There is no attachment to the tibial
sesamoid.
Action: Flexes the ankle joint; extends the hal-
lux, with eversion of the foot.
M. peronaeus longus (figs. 101-103, 139) arises
by mingled fleshy and tendon fibers from a small
area on the anterolateral surface of the head of the
fibula and an adjacent area on the lateral condyle
of the tibia. The muscle becomes tendinous near
the distal end of the fibula. The tendon passes
over the tendons of the other peroneal muscles,
to insert into the base of the fifth metatarsal just
posterior to the insertion of the peroneus brevis.
Action: Everts and abducts the foot.
M. peronaeus brevis (figs. 101, 102, 139, 140)
arises from the lateral surface of the shaft of the
fibula throughout its distal three fourths. The
muscle becomes tendinous after passing through
its groove in the lateral malleolus of the fibula.
The tendon exceeds those of either of the other two
peroneal muscles in size, and inserts into the dorsal
surface of the base of the fifth metatarsal.
Action : Everts and abducts the foot.
M. peronaeus tertius (figs. 101-103, 139, 140)
is a very slender muscle lying on top of the much
larger peroneus brevis. It reaches the fibula only
at its extreme proximal end. The muscle forms its
terminal tendon at the distal end of the fibular mal-
leolus, beneath the transverse tarsal ligament. The
tendon is somewhat smaller than that of the pero-
neus brevis, immediately in front of which it lies;
it extends to the base of the basal phalanx of
digit 5, gradually coming to lie dorsad instead of
laterad, and joining the tendon of the extensor
digitorum longus.
Action: Everts and abducts the foot.
D. Muscles of the Foot
M. extensor digitorum brevis (figs. 101, 103)
has the usual origin from the coracoid process of
the calcaneus. Its structure is complex, but it
forms four more or less distinct digitations that
go to digits 14. That to the lateral side of digit 4
is the most distinct, and is the only one that forms
a well-defined tendon. Each of the others bifur-
cates at the metatarso-phalangeal articulation, to
supply adjacent sides of two digits by means of a
tendinous expansion. There is some insertion of
muscle fibers into the deep surface of the tendons
of the extensor digitorum longus, but the tendons
of the two muscles remain distinct.
Action : Aids the long extensor in extending the
toes.
Fig. 103. Muscles of the right leg of Ailuropoda, anterior view.
192
DAVIS: THE GIANT PANDA
193
Lig. plant arum prof.
M. flex, hallucis brevis
Tuber calcanei
Mm. adductores digitorum
M. flex. dig. quinti brevis
(pars med.)
M. flex. dig. quinti brevis
(pars lat.)
Fig. 104. Muscles of the plantar surface of the right foot of Ailuropoda.
M. flexor hallucis brevis (figs. 102, 104) is a
powerful, complex muscle. It is composed of a
very small internal part, and a large bipennate ex-
ternal part. The internal part arises from the
plantar ligament in common with the external part,
and extends as a very short muscle belly to its in-
sertion on the inner side of the base of the first
phalanx. The external part arises from the tibial
sesamoid, from the navicular and cuneiform bones,
and from the plantar ligament. It inserts into
the outer side of the base of the first phalanx of the
hallux.
Action: Flexes the hallux.
M. abductor digiti quinti (figs. 101, 102, 140)
is a slender fleshy band of muscle arising from the
lateral and ventral sides of the distal end of the
calcaneus. Insertion is into the tuberosity of the
fifth metatarsal, just proximal to the insertion of
the peroneus brevis.
Action: Abducts the fifth toe.
M. flexor digiti quinti brevis (figs. 102, 104)
is a powerful muscle occupying the entire plantar
surface of the fifth metatarsal. It is partly sep-
arable into a small medial part and a much larger
lateral part. The lateral part, in turn, has a bi-
pennate structure. The fibers of the median part
arise from a small area on the ventral surface of
the cuboid, and this part of the muscle inserts into
the medial metatarso-phalangeal sesamoid. The
lateral part of the muscle arises from the cuboid,
and from the sheath of the peroneus longus along
nearly the entire length of the metatarsal. This
part inserts into the lateral sesamoid.
Action : Flexes the basal phalanx of the fifth toe.
194
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Astragalus
Os sesamoid, tib
Os metatarsal 1
Calcaneus
Os metatarsal 5
Phalanx 5
Fig. 105. Interosseous muscles of right foot of Ailuropoda.
M. flexor digitorum brevis (figs. 102, 140)
arises as a continuation of the aponeurosis of the
plantaris and from the deep surface of the plantar
aponeurosis. It consists of a fleshy belly that di-
vides into four digitations distally, that going to
the fifth toe being the largest. At the proximal ends
of the metatarsals the digitations form slender ten-
dons, which are distributed to digits 2-4. These
tendons are perforated by the tendons of the fiexor
digitorum longus at the metatarso-phalangeal ar-
ticulations. Insertion is into the second phalanx.
Accessory slips, four in number, pass from the
superficial surface of the conjoined long flexor ten-
don to the tendons of the flexor brevis; a few of
the most superficial fibers come from the quadratus
plantae. These slips decrease in size from the fifth
to the second, and each inserts into the medial side
of the corresponding tendon of the flexor digito-
rum brevis.
Action : Flexes the middle and basal phalanges
of digits 2-5.
M. quadratus plantae is a wide band arising
from the lateral surface of the shaft of the calca-
neus, and extending obliquely across the sole to
its insertion on the superficial surface of the con-
joined long flexor tendon. The muscle is shot
through with tendon fibers, which unite toward
the insertion into a central tendon into which the
muscle fibers insert in bipennate fashion.
Action: Assists the long flexor in flexing the toes.
Mm. lumbricales(fig. 102), fourin number, arise
from contiguous sides of the digital slips of the
conjoined long flexor tendon. They insert on the
DAVIS: THE GIANT PANDA
195
medial sides of the bases of the fii-st phalanges of
digits 2-5, that to the fifth digit being the largest.
Action: Flex the basal phalanges of digits 2-5.
Mm. adductores (fig. 102) are three bellies on
the sole, arising together from the deep plantar
ligament and the underlying tarsal bones. The
largest and most medial belly is double, and goes
to the inner side of the base of the first phalanx
of digit 1. The middle belly goes to the lateral
side of digit 2. The lateral belly goes to the lat-
eral side of digit 4.
Action: Flex the basal phalanges of digits 1, 2,
and 4 and draw them toward the midline of the
foot.
Mm. interossei (fig. 105) are made up of three
groups of muscles arising from the plantar liga-
ment and the bases of the metatarsal bones, and
inserting into the bases of the proximal phalanges.
The first and most medial is a single large inde-
pendent slip arising between the first and second
metatarsals at their bases and going to the medial
side of digit 2. The second arises beneath the
second metatarsal, slips going to both sides of
digit 2 and to the medial side of digit 3. The third
arises beneath the fourth metatarsal, and goes to
both sides of digits 3 and 4.
Action: Flex the phalanges on the metatarsals.
E. Review of Muscles of Hind Limb
The muscles of the hind limb in Ailuropoda, like
those of the fore limb, agree closely with the corre-
sponding muscles of the bears in gross structure.
As in the fore limb, correspondence often extends
down to minor details. In the tabulation of myo-
logical characters (p. 197), the giant panda and
the bears are in complete agreement.
As in the fore limb, comparison of the relative
masses of individual muscles reveals subtle differ-
ences among representative carnivores (Table 15).
These differences are less obviously correlated with
functional requirements than was the case in the
foi'e leg, and agreement between Ailuropoda and
the bears is less close than in the muscles of the
fore leg. In the cursorial dog the extensors of
the thigh (adductors) and flexors of the leg (biceps)
are dominant, whereas in the bears and the giant
panda no single muscle stands out, and muscles
that adduct, abduct, and rotate are more impor-
tant than in the dog. As in the fore limb, the lion
tends to be intermediate.
The weight relations between fore and hind
quarters are significantly different in Ailuropoda
from those in other arc told carnivores (Table p. 196;
data as in Tables 14 and 15). In the panda the
hind quarters are relatively lighter (or the fore
Table 15. RELATIVE WEIGHTS OF MUSCLES OF THE HIP AND THIGH IN CARNIVORES
Ailuropoda*
Wt. in
gms. %
Iliacus and psoas 121 7.2
Glutaeus superficialis 123 7.3
Glutaeus medius 136 8.1
Glutaeus profundus 21 1.2
Tensor fasciae latae 21 1.2
Obturator internus 14 .8
Gemellus anterior 1 .1
Gemellus posterior 3 .2
Piriformis 15 .9
Quadratus femoris 20 1.2
Obturator externus 42 2.5
Semimembranosus 148 8.8
Semitendinosus 91 o.4
Sartorius 114 6.8
Rectus femoris 76 4.5
Vastus lateralis \ 1-7 qs
Vastus intermedius J
Vastus medialis 91 5.4
Pectineus 33 2.0
Gracilis 115 6.8
Adductor 146 8.7
Biceps 199 11.8
Tenuissimus
Totals 1687 100.2
* Half-grown individual.
'* Data from Haughton.
Tremarclos
Ursus
Cams
Wt. in
americanus**
familiaris"
Leo leo'
gms.
%
%
%
113
4.7
4.8
4.5
10.6
85
3.6
4.7
1.7
1.6
158
6.6
5.9
7.3
6.6
20
1.0
.4
.8
1.1
52
2.2
2.5
4.1
3.0
17
.8
1.8
2
5
.2/
1.3
1.3
13
.5
.9
.6
1.1
12
.5
.7
.5
.7
49
2.1
8.3
1.0
1.2
281
11.8
4.7
4.6
12.0
96
4.0
4.3
6.8
4.6
149
6.3
5.1
1.9
5.4
174
7.3
6.3
5.0
5.0
/221
9.3
'i)
10.8
I 50
2.1
14.6
57
2.4
3.3
5.8
28
1.2
1.6
.6
.3
158
6.6
6.1
4.6
4.1
276
11.6
14.6
22.5
13.7
360
15.1
15.4
16.4
12.6
6
.3
100.3
100.0
100.8
2382
100.0
196
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
RELATIVE WEIGHTS OF MUSCLES OF FORE AND HIND QUARTERS IN CARNIVORES
Ailuropoda*
Trernarclos
Ursus**
Cams"
Leo'
gms. %
gms. %
gms. %
%
%
Shoulder and arm
1132 40
1309 35
1607 36
34
34
Hip and thigh
1687 60
2382 65
2891 64
66
66
' Half-grown individual (Su Lin).
* Data from Haughton.
quarters heavier) and there is no obvious func-
tional reason for this altered relationship, which
agi-ees with the relationships found in the skeleton.
It probably reflects a generalized increase in the
mass of muscle tissue in the anterior part of the
body (p. 182).
V. DISCUSSION OF MUSCULAR SYSTEM
The data on the muscular system may be con-
veniently considered under two heads: taxonomic
characters, and evidence for the operation of evo-
lutionary mechanisms. It is not intended to im-
ply that these two kinds of data are unrelated to
each other.
Taxonomic Characters
The musculature of the Carnivora fissipeda was
reviewed in detail by Windle and Parsons (1897,
1898). The viewpoint of these authors was purely
morphological. They summarized the literature,
supplemented it with many original dissections,
and critically analyzed the resulting mass of data
for features that characterize the order Canivora,
or that characterize families within the Carnivora.
They had data on 55 individuals, representing 25
species, of arctoid carnivores.
The accompanying table (Table 16), expanded
from the summary table of Windle and Parsons,
summarizes the musculature of the arctoid carni-
vores from the morphological and taxonomic stand-
points. Consideration of the facts in Table 16
yields the following conclusions:
1. The Canidae appear to differ from all other
arctoids more than any of the latter do among
themselves. But the features peculiar to the Cani-
dae are, apparently without exception, adaptations
to cursorial locomotion and therefore do not repre-
sent deep-seated primary differences. Practically
every one of the canid characters is shared with
the likewise highly cursorial Hyaenidae, to which
the dogs are only remotely related.
2. The Mustelidae differ among themselves more
than do the members of any other family. Never-
theless two features appear to characterize all mus-
telids: the presence of the deep rhomboid as a
distinct muscle,' and the presence of an extra head
' This is present in Potos, which shares many other ana-
tomical features with the Mustelidae.
of the triceps, arising from the angle of the scap-
ula. Both of these appear to be deep-seated, long-
standing features.
3. The Ursidae and Procyonidae resemble each
other more than either resembles the Canidae or
Mustelidae. For the most part this resemblance
is merely the absence in both of specializations
such as characterize the dogs and mustelids; in
other words, the bears and procyonids share gen-
eralized carnivore features.
4. The Ursidae and Procyonidae differ in a
number of minor characters. These are not obvi-
ously correlated with functional differences, nor is
the pattern of the musculature notably more spe-
cialized in one family than in the other.
5. Ailuropoda does not differ from the Ursidae
in a single myological character (see above for a
discussion of the biceps). Indeed, the resemblance
is much closer than the table implies. The pattern
of the musculature strongly supports the conclu-
sion that the giant panda is closely related to
the bears.
Myological Evolution
Although the pattern of the musculature in the
giant panda is practically identical with that of
the bears, the musculature differs in other impor-
tant ways. These differences must be accounted
for before we can claim to understand the anatomy
of the giant panda. They are:
1. Regional hypertrophy of the musculature.
2. Differences in the relative mass of the individual muscles.
3. Differences in internal muscle structure.
4. Differences in attachment sites
1. Available data show significant size differ-
ences between Ailuropoda and the bears in whole
regional muscle masses. These regional masses
appear to be moi-phological units rather than func-
tional units: in the head all muscles derived from
the mandibular ai-ch are hypertrophied, regardless
of function, whereas muscles of other embryonic
origin are unaffected, even though they lie in the
same general area of the head. Thus in this in-
stance the morphological unit is also a develop-
mental and genetic unit.
The case for the limb musculature is less clear.
The ratio between fore quarter weight and hind
s
a
T3
4J
C4
"3
>>
c
qJ
4J
OJ
^
m
ei3
cfi
3
s
0)
s
3
a
O
S
c
QJ
o
OT
J2
o
J2
a
c
o
c
QJ
a
g
o
o c
C m
K "1
4J
c
1
as
3
bo
a
Is
a.
C
tn
73
o
OJ
w
3
<u
a;
1
c
a
J2
3
a
&
s.
O
>
t (
<
Q
o
PLI
s
^ a)
oq
a
T3
S
u.
-M
OS
C
?
IS
c
0}
-W
OJ
L.
-4J
j=
c
Q.
T3
m
3
fc-.
a
o
*->
o
0)
1
o
o
*->
o
>,
c
c
CO
i
T3
a
a)
c
"5
O
en
'>
1
s
o.
o
J2
3
_aj
3
c
ca
>
B
c
o
rt
o
c
-M
QJ
-tJ
aj
c
S
J3
.S2
C
a;
a>
J3
.a
C
^
>
1^
O
n
o
J3
o
ja
_o a D.
a a
c S ^
^
c
a
J2
a
e
a)
OS
OS
ss
-!-
>>
>.
aj jD
c
^
^
SR o!
a>
ca
o
a
m
3
3
c
J2
tn
3
3
I i
S a
XI
3
O
a
c 5
o. a
a) a) aj 0)
m w tn tn
O) a> aj aj
fc b "^ b
Q. O. O. O.
o
H
o
00
00
o
e
CM
o
B
CS
T3
B
E
T3
O
o
o
3
n
<
Q
a;
e
c
o
S S
a
a
B
CIS
O
T3
ca
S o
a ^
o
-M
g
g
J=
tn
a;
^
B
o
s ca
n! a)
3J=
o
3 2 E
E i-o
O
pq
a
tn
3
bd
B
O
J3
O
o
B
o
m
3
4^
B
a)
-3
en
T3
-M
^
X
ca
E
a>
B t,
a) a3
M
B
wi5
og.
B
O
a
CO
B
3
4J
fi
a;
B
a;
a;
a;
to
ca
o
X
a
^
c
B
_>>
te
Ui
M
V
ca
X
>
3
tn
0)
o
3
"2 CO
S^
a. 2
>^
o o
Xi
ca
43 +J -M
n a
T3
4^
a;
o
a ca
XI
ca
ca
i 3
a ^ d 3
a
ca
Sf^ -
o ^ -
a) j3
>> ca
X:
ca
5
ca tj a) c
W tS Ph
4=
o
a> T3
D. E
3 3
tn r-
B S "
.2-0 .2
" ca j3
2 ^ 2 ^ S
m [X. Cm
T3
3
XI
C3
XI
ca
ca
ca
E S ^
cp to ^
x>
C3
B a)
aj >-c^
tn bo
a> B
D. to
^ "s g
3 3m
tn 2 -D
3 3 ca
_cr
"a
to
cr
c
s
^
?
"
c<
is
.2 B Ji
^ ^
i: Q. -a
2 >. ^ 4.
fc- ca ca aj
u 3 3 to
+j 3 -3 ca
T3
ca
a>
"ca
T3
3
ca
2 .2 B
3 L^ a>
2 o -^
3 ti E
O M M
B B B B
a) aj a> a;
CO to CO tn
a) a) a) 0)
^ ^ ^ b
0,0,0.0.
B B B B
O) aj aj a)
tn tn tn tn
O) aj a) a;
tn M t. Im
o. o. o. o.
4^ 4-3 4J 4.3
B B a B
aj a; a) a;
tn CO CO CO
a; a; aj aj
^ ^ t~< t^
o. a o, a
J2
ca
_>.
"ca
3
X
ca
a
a>
a
bo
3
O
ca
a
CO
3
4->
ca
u
o
ca
3
lo 2
o5 55
B -2
tn 'o
O CQ
S I
1 I
E E
3 3
ca ca
2 ^ -a Q Q
197
198
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
quarter weight in Ailuropoda clearly differs from
that in other carnivores examined, and this seems
to involve the total musculature rather than indi-
vidual elements. The difference is far less than for
the craniomandibular musculature, but is never-
theless considerable. It is impossible, from our
data, to determine what, if anything, is involved
morphogenetically.
2. It is well known that in the individual a
muscle hypertrophies as a result of continuous
exercise and atrophies with disuse. It has been
shown experimentally that the relative sizes of
muscle elements depart significantly from the norm
when the forces to which they are habitually sub-
jected are changed (e.g., Fuld, 1901). Therefore
observed differences in the relative size of a given
muscle, even when consistent in all individuals of a
species, may simply reflect the response of that
muscle to extrinsic mechanical forces rather than
the action of factors intrinsic to the musculature.
No morphogenetic mechanism capable of produc-
ing selective hypertrophy of individual muscles
has so far been demonstrated.
Differences of this kind occur in the musculature
of Ailuropoda as compared with that of the bears.
Involved are both craniomandibular and limb ele-
ments. The observed differences are no greater
than those distinguishing Fuld's bipedal dogs from
his normal controls, and may therefore represent
factors extrinsic to the musculature. There is at
present no known way of determining whether
such differences depend on factors intrinsic or ex-
trinsic to the musculature.
3. Differences in internal muscle structure in-
volve arrangement of fibers, form and extent of
tendons and tendinous aponeuroses, length and di-
ameter of fibers, etc. Obviously, profound changes
of this kind must have occurred during the phy-
logeny of vertebrates. The only such difference
of any importance observed in the present study
was the tendinization of fascial planes in the tem-
poral muscle of Ailuropoda. The extent to which
such a difference reflects changes in the genetic
substrate is unknown.
4. There is considerable variation in the attach-
ment sites of muscles among the carnivores, and
these differences usually shift lever advantages in
the direction of either speed or power and so are
broadly adaptive. Such differences must surely
result from the action of selection on genetic sys-
tems, but they scarcely exist between Ailuropoda
and the bears and therefore need not concern us
here. The only notable differences in attachment
sites between these two groups failure of the ab-
ductor pollicis longus and tibialis posterior to reach
the first metapodials have a purely mechanical
cause. The tendons of these muscles already at-
tach partly to the radial and tibial sesamoids, re-
spectively, in bears. Further enlargement of the
sesamoids in Ailuropoda has simply blocked the
tendons off from the metapodials.
VI. CONCLUSIONS
1. The musculature of Ailuropoda is almost
identical with that of the Ursidae.
2. Only two significant differences are evident:
hypertrophy of the craniomandibular musculature,
and failure of the abductor pollicis longus and tibi-
alis posterior to reach their normal attachment sites
on the first metapodials.
3. Hypertrophy of the jaw muscles is associ-
ated with hypertrophy of all muscles derived from
the mandibular arch, and extends in a decreasing
gradient to the musculature of the neck, shoulders,
and upper arm. This condition has a direct, and
probably very simple, genetic base.
4. The abductor pollicis longus and tibialis pos-
terior are prevented mechanically from reaching
their respective metapodials. The cause for the
condition in the panda is therefore extrinsic to the
muscular system.
5. Differences in the relative sizes of individual
jaw and limb muscles are evident. Some, prob-
ably all, are adaptive, but whether the causes for
these differences are intrinsic or extrinsic to the
muscular system cannot be determined from our
data.
ALIMENTARY SYSTEM
I. MOUTH
The hard palate (fig. 106) is narrow and elon-
gate. Its lateral borders are nearly straight, al-
though there is a slight expansion opposite the
fourth premolar and first molar. There are 10 pairs
of low palatal ridges, rounded rather than V-shaped
in cross section, which meet a faint longitudinal
ridge running down the midline. Only the first
pair of ridges is transverse; successive pairs are
progressively more obliquely displaced, and less
and less sharply set off from the surrounding tis-
sue. The last ridge is at the level of the posterior
border of the first molar. There is a prominent
incisive pad between the incisor teeth and the first
pair of palatal ridges. The palate of a second indi-
vidual (Mei Lan) is similar except that the ridges
are even less prominent.
The soft palate has a length of 105 mm., end-
ing posteriorly in a square free border, the velum
palatinum. Numerous punctures, representing the
openings of the palatine glands, are distributed
over the anterior part of the soft palate and the
extreme posterior part of the hard palate.
The entire palate is unpigmented.
In specimens of Ursus tibetanus, Tremarctos or-
natus, Ailurus fulgens, and Procyon lotor the pala-
tal sculpturing is much more prominent than in
Ailuropoda, which looks almost degenerate in com-
parison. The palatal ridges number 8-10, and are
V-shaped in cross section and much larger and
sharper than in the giant panda. They are also
more transversely situated.
II. SALIVARY GLANDS
The parotid gland (figs. 107, 108) is roughly
rectangular in form, its height considerably ex-
ceeding its width. It is quite extensive, the main
part of the gland measuring approximately 90 mm.
by 50 mm. The entire gland, with its duct, weighs
57 grams. The gland fills the area between the
posterior border of the head posteriorly, a line pro-
jected along the upper teeth ventrally, and the
posterior border of the masse ter muscle anteriorly;
dorsally it extends well up onto the ear cartilage.
The dorsal border of the gland is concave, with
moderately well-marked pre-meatal and post-
meatal processes. The posterior border is nearly
straight, but is produced slightly backward at its
ventral angle by the underlying internal facial
vein. The ventral border is somewhat irregular;
it is molded around the submaxillary gland to give
a general concave contour. The anterior border
is convex.
The gland is much flattened. It is divided into
rather small leaf-like lobulations. The parotid duct
emerges below the center of the gland, by a dorsal
and a ventral root that promptly unite. The sub-
stance of the gland is carried forward along the
duct on the right side of the head, and small acces-
sory lobules are distributed along the length of the
duct on both sides of the head as far as the labial
commissure. These lobules open separately into
the parotid duct by short ducts of their own. The
main parotid duct runs horizontally across the
outer face of the masseter, passes internal to the
external facial vein at the anterior border of the
masseter, to terminate in the cheek near the gum
line, opposite the posterior part of the fourth pre-
molar (carnassial).
The submaxillary gland (figs. 107, 108) is reni-
form, with the concavity directed caudad. It meas-
ures approximately 50 mm. in height and 35 mm.
in width. The entire gland, with its duct, weighs
19 grams. Its surface is nearly smooth, the lobu-
lations being much shallower and more regular
than are those of the parotid.
The gland is in contact with the parotid dor-
sally. Its medial border rests on the sternohyoid
muscle. Immediately in front of it is a pair of
lymph glands, one on either side of the external
facial vein.
The submaxillary duct leaves the deep surface
of the gland slightly above its center. It passes
forward between the digastric and masseter mus-
cles, then deep to the mylohyoid where it runs
along the medial border of the sublingual gland.
Beyond the anterior end of this gland it parallels
the sublingual duct to the caruncula sublingualis,
where the two ducts open side by side. The sub-
lingual carunculae are a pair of very prominent
papillae, 4 mm. in diameter, situated on the floor
of the mouth. They are located 10 mm. anterior
to the frenulum of the tongue, and the two carun-
culae are 9 mm. apart.
199
200
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Papilla incisiva
Opening of Ductus nasopalatlnus
Palatum durum <
Palatum molle <
.Raphe palati
Rugae palati
Openings of Gl. palatini
Ostium pharyngeae tubae
Ostium bursae pharyngae
Fig. 106. The hard and soft palates of Ailuropoda.
expose the entrances to the pharyngeal bursae.
A window has been cut in the posterior part of the soft palate to
The greater sublingual gland (figs. 107, 108)
is elongate and irregular in outline, triangular in
cross section posteriorly, and much flattened an-
teriorly. It is wider posteriorly than anteriorly.
An irregular vertical arm is continued up along the
submaxillary duct, around the digastric muscle, to
the anterior border of the submaxillary gland, with
which it is in contact. The main part of the gland
(exclusive of the vertical arm) measures 92 mm. in
length, with a maximum width of only about 10
mm. It occupies the lateral sublingual space, and
is in intimate contact with the mylohyoideus ven-
trally. It extends from the level of the angular
process of the mandible forward to the posterior
border of the first lower molar.
The duct may be traced through the substance
of the gland, occasionally appearing on its lateral
surface. It leaves the gland at its anterior tip,
I
DAVIS: THE GIANT PANDA
201
A. & N. supraorbital is
.V. lacrimalis
A. & v. auric, ant.
R. auric, aiit. N. facialis
M. auric, ant. inf.
M. lev. auris long.
VII: N. zj/gomaticoteoiporalis
A. & N*. frontalis
V. ophthalmica superior
.V. supratroch.
N. infratroch.
V. nasofrontalis
A. & V. annularis
Orificium ducti parotidei
A. & N. infraorbital is
A. & V. labialis su(>erf.
y. nasal is
externa
Ductus parotideiis
Gl. parotis
IN. auric, magnum
N.buccolis^perioT.
N. buccali^ inferior^
Gl. subling. major '
Gl. submaxillaris.
Ductus submazillaris
X. cutatteus colli
V. facialis interna
V. jugularis externa
V. facialis prof.
R. m. platysma
V. anast. V. labialis inf.
A. maxillarU externa ^- * ^- '"'"'^''^ '"^
Fig. 107. Superficial dissection of the head of Ailuropoda.
and parallels the submaxillary duct to the sublin-
gual caruncle, where it opens.
The lesser sublingual glands (fig. 108) are
represented by glandular masses situated just deep
to the greater sublingual gland, and extending from
the posterior border of the greater sublingual gland
to the base of the tongue, a distance of 43 mm.
Dorsally they are continuous with the palatine
glands, and ventrally there is no boundary sepa-
rating them from the inferior alveobuccal glands.
The palatine glands consist of a layer of lob-
ulated glandular tissue under the mucous mem-
brane of the soft palate and the posterior end of
the hard palate. Laterally they are continuous
with the lesser sublingual glands. Numerous dots,
distributed like pin-pricks over the mucous mem-
brane of the soft palate and the posterior part of
the hard palate (fig. 106), represent the outlets
of these glands.
The inferior alveobuccal glands (molar gland)
(figs. 107, 108) are well developed. They may be
traced on the medial side of the mandible from the
symphysis (at the posterior border of the third pre-
molar) back to a point beyond the last molar ; the
gland mass gi'adually increases in size posteriorly.
Behind the last molar it crosses over to the outside
of the mandible, where it is continued forward on
the buccinator muscle and deep to the masseter to
the labial commissure. Each of the glandular ele-
ments opens by an independent duct. There are
numerous outlets, hardly visible under a magnify-
ing glass, in the mucous membrane below the teeth
on the inner side of the mandible. A double row
of 24 or more prominent papilla-like projections,
ranging up to a millimeter in diameter, in the
mucous membrane of the cheek near the lower
molar teeth, mark the outlets of the extra-man-
dibular part of the gland mass.
The orbital glands (fig. 108) form a compact
ovate mass of 12-14 independent but closely asso-
202
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Orbitoparotideus,
Sublingualis minor
Ductus submaxillaris
Fig. 108. Salivary glands of Ailuropoda, semi-diagrammatic.
dated elements situated in the suborbital space
immediately above the last upper molar. The
much-flattened gland mass lies between the bone
and the temporal muscle. It measures 37 mm. in
length by about 18 mm. in height. The dozen or
more ducts open on low, inconspicuous projections
that are scattered over a fold of the oral mucous
membrane laterad of the posterior half of the last
upper molar.
The orbitoparotid gland (fig. 108) is a small
structure situated at the inferior corner of the an-
terior root of the zygoma. It is bounded, as usual,
by the anterior border of the masseter posteriorly,
the parotid duct dorsally, and the buccinator mus-
cle and oral mucous membrane internally. The
gland measures about 10 mm. in diameter. The
duct parallels the parotid duct to a point opposite
the middle of the second upper molar, where it
opens on a minute papilla near the lateral border
of the tooth.
Carmalt (1913) described and compared the gi-oss
structure of the salivary glands in eight species of
fissiped carnivore: Canis familiar is, Procyon lotor,
Ursus tihetanus, Taxidea taxus,Gulo luscus, Mephi-
tis mephitica,Felis domestica, andF. leo. The liter-
ature on these glands was reviewed extensively by
Fahrenholz ( 1937). In general the salivary glands
are relatively small in cai-nivores, particularly the
serous ( parotid) glands, which may be smaller than
the submaxillary gland in predominantly flesh-eat-
ing forms. Carmalt concluded that the form of
the salivary glands in carnivores is determined
largely by the molding effect of surrounding tis-
sues, and therefore that differences in shape are of
no great significance. The parotid gland tends to
be large in herbivorous mammals. Among the
Carnivora it is large in the bears, immense in Pro-
cyon (Fahrenholz), "considerably larger than the
submaxillary gland" in Ailurus (Carlsson, 1925).
These are among the most herbivorous of the car-
nivores. It is small in the Canidae.
Ailuropoda resembles other herbivorous carni-
vores in its large parotid gland. The relative size
of this gland (twice the size of the submaxillary) is
comparable to the condition in bears, but is far
short of the relative size in Procyon, in which the
parotid is six times the size of the submaxillary.
III. TONGUE
The tongue (fig. 109) is of moderate length and
narrow, and is devoid of pigmentation. It meas-
ures 210 mm. from tip to base, and 55 mm. in
greatest width. The lateral margins of the oral
part are nearly parallel, although the organ tapers
slightly toward the tip. There is a prominent
frenultun on the inferior surface, situated 75 mm.
from the tip. There is a small but distinct median
notch at the tip, but no indication of a median fur-
row on the dorsum. The glosso-epiglottic furrow,
on the other hand, is very well marked.
M. cricoaryt. post.
M. constrictor pharyngis med
Recessus pyriformis
Plica vocalis
M. constrictor pharyngis ant.
Os tympanohyale
Papillae vallatae
N. laryngeus inf., R. ant.
Rima glottidis
Epiglottis
Sulcus glosso-epiglotticus
Tonsilla palatina
Gl. sublingualis
Fig. 109. Upper surface of tongue of Ailuropoda.
203
204
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Conical papillae cover the entire dorsum from
the tip back to the epiglottis. They are quite uni-
form in size except near the tip, where they are
sHghtly larger, and in the pharyngeal region where
they are much larger and sparser. Large conical
papillae are also present on the under surface at
the tip and for 65 mm. along the lateral margins.
Fungiform papillae are distributed over the
entire dorsum of the oral part of the tongue, ex-
cept for a small area along the midline 30 mm. long
and about 5 mm. wide, and situated about 20 mm.
back from the tip, where they appear to be absent.
They are very conspicuous and are evenly spaced
at intervals of 2 to 3 mm., posteriorly showing a
tendency to form diagonal rows running from the
midline outward and backward. They are not ab-
sent over the entire middle of the dorsum, as Raven
found in the tongue he examined.
The vallate papillae are arranged in a semi-
circle, and not in V formation as Raven suggested.
There are thirteen papillae; in some cases a small
secondary papilla is closely approximated to a
larger one and enclosed in the same fossa (these
were not counted in arriving at the total) . In addi-
tion there are three papillae situated irregularly
behind the row on the right side, making a total
of sixteen. Raven postulated seventeen as the
number originally present on the incomplete tongue
he examined.
Foliate papillae are absent. Raven identified
as foliate papillae two longitudinal slits, asym-
metrically placed on the anterior dorsum of the
tongue. A single such slit is present on the dor-
sum near the tongue tip in our specimen. This
slit is not glandular and quite evidently represents
a mechanical injury.
The lyssa is a small structure, 33 mm. long by
about 2 mm. in diameter, situated in the anterior
part of the tongue. Its length is thus about 16
per cent of that of the tongue as a whole. The
structure, which is oval in cross section, is attached
to the mucous membrane at the tip of the tongue
anteriorly. Posteriorly it is continued into a thin
cord that is lost in the lingual septum.
The gross structure of the tongue in the Carni-
vora was reviewed by Sonntag (1923), and again
by Stadtmiiller (1938). Among the Procyonidae
and Ursidae, differences appear to involve prima-
rily the number and distribution of the papillae.
The fungiform and conical papillae diflFer little from
conditions described here for Ailuropoda. In the
procyonids and bears the number of vallate papil-
lae ranges from six to twenty, the larger numbers
occurring in the bears. They are more numerous
in bears than in any other carnivore. The vallate
papillae are arranged in a V, except in certain bears
( Ursus americanus, Helarctos malayanus) in which
they are described as forming a semicircle. The
Ursidae and Ailuropoda agree in the large number
of vallate papillae, and only in these forms do they
ever form a semicircle.
According to Stadtmiiller the number of vallate
papillae in mammals is not correlated either with
diet or with degree of development of the sense of
taste, but tends to be larger in less primitive forms.
Nimiber and arrangement are consistent at or be-
low the family level.
Statements on the foliate papillae are very con-
tradictory. Sonntag found no trace of them in
Procyon cancrivora, Nasua narica, Polos, or Ailu-
rus, but observed "some small foliate clefts" in
Procyon lotor. Stadtmiiller failed to find them
in Nasua rufa and Potos. Carlsson says they
"stand out prominently" in Ailurus. I could find
no trace of foliate papillae in Procyon lotor.
Among the Ursidae, Sonntag observed "small
foliate clefts" in Thalarctos and Melursus, and
Tuckerman described foliate papillae for Ursus
americanus and Helarctos. Stadtmiiller, on the
contrary, could find no foliate papillae in Ursus
tibetanu^, Helarctos, and Thalarctos. I failed to
find them in Ursus tibetanu^.
The lyssa, which is large in the Canidae, is pres-
ent but small in all ursids and procyonids except
Potos, in which it is said to be large.
The tongue appears to differ little among the
Procyonidae and Ursidae. The tongue of Ailu-
ropoda most closely resembles that of Ursus.
IV. PHARYNX AND ESOPHAGUS
A. Pharynx
The pharynx is relatively capacious. The naso-
pharynx and pharynx proper together have a total
length of about 135 mm., and the width just back
of the velum palatinum is about 40 mm. (with the
walls flattened out). The pharynx is fusiform in
shape, tapering gradually toward the choanae an-
teriorly and the esophagus posteriorly. The pars
nasalis pharyngis is 115 mm. long, thus greatly
exceeding the pharyngis propria, which measures
only about 20 mm.
A pair of openings, the outlets of the bursae
pharyngeae, is situated in the dorsal wall of the
nasopharynx (fig. 106). These openings are lo-
cated 12 mm. anterior to the ventral border of
the foramen magnum and 35 mm. anterior to the
posterior border of the velum palatinimi; they lie
immediately in front of the anterior border of the
pterygopharyngeal division of the anterior con-
strictor muscle of the pharynx. They are a pair
of crescent-shaped slits, 7 mm. in length, separated
DAVIS: THE GIANT PANDA
205
by a prominent isthmus 5 mm. in width. The
right slit is more prominent and opens into a ca-
pacious thin-walled sac, 130 mm. long by 30 mm.
in greatest width (flattened out), situated between
the esophagus ventrally and the longus colli mus-
cle and centra of the cervical vertebrae dorsally
(fig. 110). The bursa, lying in the trough bounded
laterally by the prominent longus capitis muscles,
extends caudad to the disk between the fifth and
sixth cervical vertebrae. The bursa begins with a
narrow neck, which expands into an extensive
blind sac. A very short septum divides the pos-
terior end of the bursa into right and left halves.
The left bursa, into which the left slit opens, is
much smaller, measuring only 15 mm. in length.
Proximally the lining of the large right bursa
is thrown up into prominent longitudinal ridges,
which on the lateral wall are interrupted by two
small pocket-like sinuses open anteriorly, and
slightly farther caudad by a small oval perforation
in the lining of the bursa that opens into a small
sinus. An additional pocket-like sinus is present
near the extreme posterior end of the bursa.
Killian (1888) failed to find a pharyngeal bursa
in the following carnivores: Cams familiaris, Nasua
Tufa, Mephitis mephitica, Lutra vulgaris, Herpestes
griseus, Viverra civetta, Paradoxurus trivirgatus, Felis
domestica. I have examined specimens of Procyon
lotor and Ailurus fulgens and find they have no
pharyngeal bursa.
On the other hand, the existence of pharyngeal
bursae in bears has long been known (literature
reviewed by Killian). These are described by vari-
ous authors as paired structures, always unequal
in size, with relations very similar to those de-
scribed here for Ailuropoda. Such paired bursae
have not been described for any other mammal.
Pharyngeal bursae have been described for Ursus
arctos, U. americanus, U. horribilis, Melursus ur-
sinus, and Helardos malayanus. The function of
these structures is unknown.
The openings of the auditory tubes are a pair
of longitudinal slits in the lateral walls of the naso-
pharynx at about its posterior third, 15 mm. ante-
rior to the openings of the pharyngeal bursae
(fig. 106). They are much less prominent than
the latter.
B. Muscles of the Soft Palate and
Pharynx
M. levator veli palatini is a rather narrow
band of muscle fibers arising from the petrosal im-
mediately laterad and caudad of the orifice of the
auditory tube and from the adjacent lateral wall
of the auditory tube. The muscle extends ventrad
and caudad, passing internal to the pterygopha-
ryngeus, to insert into the palate. The fibers ex-
tend to within a few millimeters of the caudal
border of the velum palatinum.
M. tensor veli palatini is shghtly smaller than
the levator. It arises, as a rounded mass of min-
gled tendon and fieshy fibers, from a groove and
ridge in the floor of the middle ear, from the scaph-
oid fossa of the sphenoid, and from the adjacent
lateral wall of the auditory tube. From its origin
the muscle passes ventrad and craniad, across the
hamular process of the pterygoid. Mesad of the
hamular process the muscle becomes tendinous,
forming a thin tendinous sheet that runs craniad
in the soft palate just inside the pterygoid process.
The tendon fibers can be traced craniad nearly to
the posterior border of the hard palate.
M. uvulae is composed of a pair of narrow bands
of muscle extending along the midline of the soft
palate and the velum palatinum. Origin is by
tendon fibers from the posterior border of the bony
palate at the midline, with accessory tendinous
slips coming from the soft palate in its anterior
quarter. The paired muscle extends caudad to
the posterior border of the velum palatimun, where
it inserts.
M. pharyngopalatinus is a thin layer of fibers
lying deep to the constrictor muscles of the phar-
ynx. It is situated at the posterior end of the
velum palatinum, where it arises from the aponeu-
rosis of the palate. From this origin the fibers fan
out over the lateral and dorsal walls of the phar-
ynx, beneath the middle constrictor and the ante-
rior part of the posterior constrictor.
M. constrictor pharyngis anterior, the small-
est of the three constrictors, is composed of three
elements, which maintain their identity through-
out. The most anterior {Pterygopharyngeus of
human anatomy) is a narrow band of fibers aris-
ing from the hamular process of the pterygoid bone.
It runs caudad to the neck of the pharyngeal bursa
and arches sharply around this structure, its most
anterior fibers forming the bulk of the isthmus that
separates the ostii bursae. The posterior part of
the muscle is overlain by the anterior border of
the middle constrictor. All the fibers of the mus-
cle pass to the dorsal midline of the pharynx, where
the muscle forms a raphe with its fellow of the
opposite side. A posterior muscle {buccopharyn-
geus of human anatomy) lies at first deep to and
co-extensive with the pterygopharyngeus. It arises
from the medial surface of the pterygoid process
and the soft palate mesad of the pterygoid process.
As the muscle passes beyond the pterygopharyn-
geus it splits into subequal parts which arch dor-
sad, embracing the pharyngopalatinus between
them, to their insertion on the dorsal midline of
206
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Os palatinum
Pars nasalis pharyngis
Os sphenoidale
Os basioccipitale
Ostium pharyngeae tubae
Ostium bursae pharyngae
Mm.constrictores pharynges
Velum palatinum
Bursa pharyngea
Pharynx propria
Oesophagus
Cart, thyreoid.
Plica vocalis
Cart, cricoid.
Trachea
Fig. 110. Sagittal section through larynx of Ailuropoda.
the pharynx. The glossopharyngeal division is a
narrow band arising from the side of the root of
the tongue at the level of the tonsils. It runs
caudad and slightly dorsad to its insertion, which
is into the lateral wall of the pharynx at the level
of the thyrohyal arm of the hyoid. Throughout
its length it lies ventrad of the other two parts of
the anterior constrictor.
M. constrictor pharyngis medius (fig. 85) is
composed of a superficial and a deep layer. The
superficial layer, which is more or less rectangular
in form, arises from the lateral surface of the thy-
rohyal. Near its insertion, where it is overlapped
by the anterior border of the posterior constrictor,
it fuses with the underlying deep layer. The deep
layer, which is considerably smaller, arises from
the posterior surface of the epihyal. Both layers
insert along the dorsal midline of the pharynx.
M. constrictor pharyngis posterior (fig. 85)
is the largest and heaviest of the pharyngeal con-
strictors. It is partially separable into an anterior
superficial part, which partly overlaps a deeper
and more caudal posterior part. The anterior
part {thyreopharyngeus of human anatomy) arises
from the oblique line of the thyroid cartilage be-
tween the superior and inferior thyroid tubercles.
The posterior part {cricopharyngeus of human
anatomy) arises from a tendinous arch extending
from the thyroid cartilage to the dorsolateral bor-
der of the cricoid cartilage, and from the entire
dorsal surface of the inferior cornu of the thyroid
cartilage. The fibers of the two parts soon become
inseparable, and the resulting common mass fans
out to its insertion, which is into the median raphe
on the dorsal side of the pharynx.
C. Esophagus
The esophagus is 35 cm. long and about 20 mm.
wide when flattened out dorsoventrally. As it
passes posteriorly from the pharynx, the esopha-
gus gi-adually moves to the left of the midline.
This deflection is greatest at the level of the third
rib, posterior to which it moves back toward the
midline, to be deflected to the left again as the
diaphragm is approached. It joins the stomach at
the level of the tenth thoracic vertebra, immedi-
ately after passing through the diaphragm. The
inner surface of the esophagus is thrown into longi-
tudinal folds which terminate abruptly at the level
of the stomach, as Raven (1936) noticed. Raven
describes the smooth epithelium lining the stom-
DAVIS: THE GIANT PANDA
Oesophagus
Cardia
207
Fundus ventrieuli
Curvatura
Curvatura minor
Lig. hepatogastricum
(omentum minor)
Lien
Sphincter pylori
Rirs pylorica.
Lig. lienorenalis
Vestibulum
Duodenum (pars anterior)
Pancreas (cervix)
Ductus choledochus
Lig. gastrolienalis
Lig. duodenorenalis
Fig. 111. Stomach, spleen, and pancreas of Ailuropoda, dorsal view.
ach as "almost horny"; such a texture is not evi-
dent in the specimen at hand.
V. STOMACH
The stomach, as Raven observed, is elongate
and slender (fig. 111). The fundus is only mod-
erately dilated, and the whole cardiac region tapers
gradually toward the pylorus. The pylorus is elon-
gate and tubular, with extremely muscular walls.
The stomach was empty in the specimen dissected;
its length along the greater curvature, from the
esophagus to the pyloric sphincter, was 400 mm.
This compares with a length of 80 cm. given by
Raven for a fully adult individual. There is a
very sharp flexure in the stomach near the begin-
ning of the pylorus, so that the pylorus is doubled
back against the cardia with its distal end near the
esophagus. The strong gastrohepatic ligament
holds the stomach in this position.
The lining of the stomach displays rather prom-
inent plicae mucosae throughout. These diff'er
considerably in diff'erent regions. In the region
of the fundus they are low and irregular, forming
an irregular reticulation. They became much
more prominent in the middle region of the stom-
ach, and show a tendency toward a longitudinal
arrangement. In the pylorus they take the form
of four elevated longitudinal folds. The mucosa
is similar over the whole stomach ; there is no corni-
fication anywhere. The wall of the pylorus is 8-
9 mm. thick. Most of this (about 6 mm.) is ac-
counted for by the tunica muscularis. Raven states
that the muscularis was only 2 mm. thick in his
specimen.
The stomach is simple in all fissiped carnivores,
with a more or less spherical fundus and a cylin-
drical, thick-walled pylorus (fig 112). The py-
lorus is characteristically doubled back against the
minor curvature. Among the arctoid carnivores
there are minor variations in form, but these have
no obvious relation to differences in diet. In Ailu-
ropoda the stomach is more elongate, particularly
the long tubular pylorus, than in any other carni-
vore examined. In bears ( Ursus americanus and
208
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Canis familiaris
Ailurus fulgens
Bassariseus astutus
Procyon lotor
Helarctos malayanus
Ailuropoda melanoleiica
Fig. 112. Form of the stomach in representative arctoid carnivores, not to scale. (Canis from Ellenberger and Baum,
Ailurus from Flower 1870, others original).
Helarctos malayanus examined) the pylorus is
rather globular in form. In an adult Helarctos
the wall of the pylorus is about 6.5 mm. thick,
almost as thick as in Ailuropoda, but the pyloric
region is far shorter than in the panda.
VI. INTESTINES AND MESENTERY
The intestines of Ailuropoda are remarkable for
their shortness and the slight differentiation of the
various regions. The fixed and preserved intesti-
nal tract, measured with the mesentery still at-
tached, was only 4780 mm. in length from pyloric
valve to anus in Su Lin. This is only four times
head and body length. In the fully adult individ-
ual studied by Raven intestinal length was 5.5
times head and body length. The gut in Ailu-
ropoda appears to be as short as in any known
carnivore.
DAVIS: THE GIANT PANDA
209
Jejuno- ileum
Duodenum
A. mesenterica ant.
A. colica ant.
A. colica med.
Colon
-A. mesenterica post.
~-A. colica post.
\. hemorrhoidalis ant.
Fig. 113. Intestinal tract and mesentery of Ailuropoda, spread out. Dorsal view.
The duodenum begins a few millimeters to the
right of the midline of the body. It turns caudad
rather abruptly at the pyloric sphincter, and I'uns
almost straight back to its juncture with the jeju-
num. There is thus scarcely any indication of the
U-shaped duodenal loop that characterizes the
arctoid carnivores. The duodenum has a length of
only 130 mm. and a diameter of about 25 mm.
The duodenorenal ligament is well developed. Its
anterior end is heavier and attaches to the tip of
the caudate lobe of the liver.
The heavy wall of the pylorus gives way abruptly
to the very much thinner wall of the duodenum at
the pyloric sphincter. Raven describes the mu-
cosa of the duodenum as thrown up into numerous
longitudinal folds. These are not evident in my
specimen; the few folds that are present corre-
spond to folds involving the entire wall of the
duodenum, and may be considered a post-mortem
effect. The lumen is lined with close-set villi, each
about 2 mm. long, which gives the lining a velvety
appearance.
The jejuno-ileum is suspended from a short
mesentery that is nearly circular in outline (fig.
113). This part of the intestine is comparatively
short, measuring only 3890 mm. in length. It is
not sharply separated from the duodenum. It
is arranged around the circumference of the mes-
entery in a series of about a dozen U-shaped loops.
The villi lining the jejuno-ileum do not differ in
appearance from those lining the duodenum. There
are no Peyer's patches, in which this specimen
agrees with the one examined by Raven.
The internal diameter of this part of the intes-
tine varies. It is about 60 mm. near the duodenum,
decreasing gradually to about 20 mm. a meter and
a half beyond the duodenum. The rest of the tract
is about 20 mm. in diameter. The mean internal
210
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
diameter of the jejuno-ileum is 28.6 mm., based
on circumference measurements made at 500 mm.
intervals on the opened and flattened-out intestine.
The internal surface area of the entire small in-
testine, calculated from the measured length of
4020 mm. and a mean internal circumference fig-
ure of 90 mm., is 361,800 mm-'.
There is no caecum, and no external indication
of the ileo-colic junction. Internally there is no
indication of a valve at the juncture between the
ileum and colon.
The colon (fig. 113) measures 580 mm. in length.
The internal diameter is about 31.5 mm., which
slightly exceeds the diameter of the lower part of
the small intestine. The colon is arranged in a
short but well-defined colic loop, which is supplied
by a separate branch of the anterior mesenteric
artery and vein, and which passes without a sharp
boundary into a short straight rectum. The rec-
tum is suspended from a narrow mesocolon, and
has approximately the same diameter as the rest
of the intestine. It has a length of 180 mm. The
lining of the rectum does not differ in appearance
from that of the colon.
The internal surface area of the colon-rectum,
calculated from the measured length of 760 mm.
and a mean internal circumference of 99 mm., is
75,240 mm-.
The mesentery from which the small intestine
is suspended arises from the dorsal midline at the
level of the last thoracic vertebra. It is nearly
circular in outline, as is characteristic of carnivores.
and is comparatively limited in extent (fig. 113).
The anterior mesenteric artery and vein cross it in
the form of a short, gently curved arc. The mesen-
teric vein gives off only four main branches in its
course across the mesentery; each of these bifur-
cates, however, about 15 mm. from its origin. The
mesenteric artery gives off seven branches; like
the veins, these bifurcate a short distance from
their origins. The anterior mesenteiic artery and
vein each give rise to a well-defined colic branch.
The colic vein arises a short distance distad of the
origin of the inferior mesenteric vein.
The pattern of the intestinal tract is simple
and extremely uniform in the fissiped carnivores
(Mitchell, 1905, 1916). Among the Arctoidea, a
caecum is present in the Canidae but absent in the
Mustelidae, Procyonidae, and Ursidae. A definite
colic loop is present in the Ursidae but absent in
other arctoids (Mitchell); a bear-like colic loop is
present in Ailuropoda.
An ileocolic valve is said to be absent in the
Procyonidae and Ursidae (Jacobshagen, 1937), but
I find a conspicuous sphincter-like ileocolic valve
in Procyon. No indication of a valve could be
found in a specimen of Ursus americanus, and
there is no valve in Ailuropoda.
The relative length of the intestinal tract varies
among arctoid carnivores (Table 17). The gut is
4-4.5 times head and body length in most arctoids.
It is longer than this in some procyonids (up to 6
times body length in Potos, 6-9 times in Procyon),
but is only 4-4.5 times in Bassariscus and Nasua.
Table 17. INTESTINAL LENGTH IN ARCTOID CARNIVORES
Head
and Body
Length
f 1217
Canis lupus < j^qqA
Canis familiaris
Bassariscus astutus [385]
Nasua socialis
Nasua sp 460
Potos flavus ( ^30
[ 594
Procyon lotor \ 490
I [530)
Ailurus fulgens < ^25
Thalarclos maritimus 1244
Ursus arctos 1352
Ursus gyas 1720
TT ! 900
Ursus amencanus ( /., -
( olo
Ailuropoda melanoleuca I ,<gg
* Evidently an error.
Lengtli
Length
Total
Intestine
Small
Colon and
Length
Head and
intestine
Rectum
Intestine
Body
Source
4870
649
5519
4100
4.5
4.1
Cuvier
Landois (1884)
1875
1920
i75
140
1525
2050
2060
5-6
4
4.5
4.5
Landois (1884)
Beddard (1898)
Carlsson (1925)
Raven (1936)
1730
2340
250
150
1980
2490
4.4
5.8
Carlsson (1925)
Raven (1936)
2700
4280
200
220
4221
2900
4500
7.1
5.9
8.7
Cuvier
Raven (1936)
Original
1620
iso
2641
1800
4.3
4.2
Flower (1870)
Carlsson (1925)
12664
10700
10510
10.1
7.9
6.1
Cuvier
Cuvier
Original
5960
4100
160*
430
6120
4530
6.8
7.4
Raven (1936)
Original
6900
4020
1100
760
8000
4780
5.5
4.1
Raven (1936)
Original
_Vena cava post.
Lobus centralis dexter
Lig. falciforme hepatis
Lobus lateralis dexter.
Lig. triang. dext.
F*rocessus caudatus
Lobus centralis sinister
Incisura umbilicalis
Lig. teres
Lobus lateralis sinister
Lobus caudatus
Lig. triang. sin.
Lobus lateralis sinister
Lig. triang. dext.
Ix)bus centralis sinister
Lobus quadratu.s
Vesica fellea
Lobu.s centralis dexter
A. hepatica
Ductus choledochus
Lobus lateralis dexter
B
Fig. 114. Liver of Ailuropoda. A, ventral, B, visceral view.
211
212
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
The gut is longest in the bears (6-10, average 7.7
times head and body length). Thus there is a
broad correlation with diet, the herbivorous forms
tending to have a longer gut (as is general among
mammals), but this is by no means a clear-cut cor-
relation in the Carnivora. In no carnivore does
gut length approach the proportions (up to 25
times head and body length in artiodactyls) found
among mammals that are primarily, rather than
secondarily, herbivorous.
The most striking lack of correlation between
diet and gut length is in Ailurus and Ailuropoda.
Ailuropoda is exclusively herbivorous and Ailurus
seems to be highly so, and yet gut length in these
is among the shortest known for the Carnivora.
VII. LIVER AND GALL BLADDER
The liver is small. Fixed in situ, it is a dome-
shaped organ, very narrow dorsoventrally and with
rather sharply arched diaphragmatic and visceral
surfaces (fig. 114). It measures 270 mm. in breadth,
and weighs 1564 grams. The liver is divided into
six distinct lobes, of which the right lateral lobe is
the largest. These are not arranged in the echelon
formation characteristic of bears and other carni-
vores. The size relations of the four principal
lobes are RL>RC>LC>LL. These relations
confirm Raven's findings.
The left lateral lobe is roughly circular in out-
line when viewed from the visceral surface. It is
more or less triangular in cross section. The free
margin is devoid of notches, which are often pres-
ent in other carnivores. A small accessory lobule
on the visceral surface near the transverse fissure
has been described in both Ailuropoda and Ailu-
rus. This structure is also present in my speci-
men, although it is hidden behind the quadrate
lobe. A heavy suspensory ligament, the left tri-
angular ligament, attaches to the dorsal margin of
the lobe and passes to the corresponding portion
of the diaphragm.
The left central lobe is approximately the same
size as the left lateral lobe, but it is more flattened
and lies mostly anterior to it; only a small triangu-
lar section of the central lobe is visible from the
visceral surface. Far below the surface of the liver
the contact surfaces of these two lobes are joined
by a prominent ligament, about 40 mm. in length,
that extends laterad from the transverse fissure.
The right central lobe is larger than either of the
left lobes, but not so large as the right lateral lobe.
When the liver is viewed from the ventral surface,
this lobe is trapezoidal in form. There is a shallow
fissure along its visceral margin near the falciform
ligament, which terminates at a short accessory
branch of the falciform ligament, extending diag-
onally across the lower left corner of the lobe. This
fissure is continued on the visceral surface of the
lobe to a point where the small ligament support-
ing the fundus of the gall bladder arises. On the
diaphragmatic surface of the liver a wide isthmus
connects the right central and right lateral lobes.
The quadrate lobe is remarkable for its small
size. It is visible only on the visceral surface of
the liver, and lies largely in a depression on the
visceral surface of the right central lobe. When
the gall bladder is inflated it hides much of the
quadrate lobe.
The right lateral lobe is the largest lobe in the
liver, exceeding the right central lobe slightly in
size. Its free margin is rounded and shows a slight
notch at the site of the triangular ligament. The
right triangular ligament, broader than the left,
connects the dorsal border of this lobe with the
diaphragm.
The caudate lobe is small but well marked, with
a poorly defined papillary process. The basal part
of the lobe lies to the left of the portal fissure as a
tongue-shaped structure, reaching to approximately
the center of the left lateral lobe. The papillary
process is separated from the basal part of the
caudate lobe by a shallow fissure to the left, from
the caudate process by a notch to the right. It is a
low, inconspicuous eminence scarcely rising above
the level of the caudate lobe.
The caudate process is continuous with the cau-
date lobe except for the notch separating it from
the papillary process. The caudate process is
sharply defined but short, extending to the right
only to about the middle of the right lateral lobe.
It embraces the vena cava as in Ursus, but lacks
the keel-shaped form characteristic of the bears
and other carnivores.
The gall bladder is an ovoid sac 55 mm. in
length. The gall bladder occupies a prominent
fossa, approximately half of which is in the right
central lobe and half in the quadrate lobe. It is
crossed diagonally by a ligament-like fold of peri-
toneum. The gall bladder is entirely visible when
the liver is viewed from the visceral surface, and
when it is distended is partially visible from the
ventral side of the liver. It is not visible from the
diaphragmatic surface, as it is in most carnivores.
The wall of the gall bladder is tough and heavy.
Internally the mucosa is thrown up into low, inter-
connected ridges, which give it a reticulated or
honeycomb appearance.
The cystic duct is arranged in a series of S-
shaped curves. A small accessory duct emerging
from the connective tissue deep to the gall bladder
but not traceable to the gall bladder itself, enters
the cystic duct 10 mm. before the latter joins the
DAVIS: THE GIANT PANDA
213
Ventral
Visceral
Bassariscus astutus
Procyon lotor
Ursus americanus
Fig. 115. Livers of representative arctoid carnivores. Not to scale.
hepatic duct. This accessory duct apparently is
homologous with the atypical "cyst-hepatic ducts"
that have been described in human anatomy. The
cystic duct joins the hepatic duct at an acute angle.
The collecting branches of the hepatic duct unite
to form the hepatic duct proper about 15 mm. from
the juncture of the latter with the cystic duct to
form the ductus choledochus.
The ductus choledochus is 95 mm. in length.
It passes through the vertical arm (caput) of the
pancreas to open obliquely into the duodenum, in-
dependently of the pancreatic duct, about 115 mm.
214
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
from the pylorus, i.e., close to the distal end of the
duodenum. The lining of the ductus choledochus
is smooth to a point about 15 mm. from its termi-
nation, that is, to its entrance into the wall of the
duodenum. Then it expands slightly to form an
ampulla (ampulla of Vater), whose lining is raised
into a series of lamelliform rings (fig. 116). The
papilla in the lining of the duodenum at the ter-
mination of the ductus choledochus is small but
conspicuous.
The comparative anatomy of the liver in mam-
mals was reviewed by Renvall (1903), Meyer (1911),
and Siwe (1937), in carnivores by Carlsson (1925).
It is evident that the mammalian liver shows con-
sistent and meaningful structural patterns, although
there is no agreement as to the causes of these pat-
terns. In all carnivores the liver is divided by
deep fissures into four principal lobes, subequal in
size: right and left lateral and right and left cen-
tral. The quadrate lobe is typically large, and lies
between the two central lobes. On the visceral
surface of the liver there is always a sixth lobe,
the caudate lobe, with a well-developed papillary
process projecting posteriorly into the omental
bursa. A large boat-shaped caudate process ex-
tends to the right of the portal fissure. The lobes
are typically arranged in echelon in carnivores,
with the two central lobes lying most anteriorly
and partly overlapping the quadrate and lateral
lobes, and the caudate lobe and its appendages
lying behind all the others. The caudate may or
may not embrace the postcaval vein.
Consistent variations on the basic carnivore pat-
tern have been described (see fig. 115). In the
Canidae the accessory lobes are large, the post-
caval vein is not embraced by the caudate lobe,
and the gall bladder is not visible from the dia-
phragmatic surface of the liver. In the Procyoni-
dae (two Procyon lotor, one Bassariscus astutus ex-
amined) the accessory lobes are as large as the
principal lobes, completely excluding the central
lobes from the visceral surface of the liver. The
quadrate is not overlapped by the central lobes on
the diaphragmatic surface. Indeed, in the Pro-
cyonidae the cystic fissure is no more than a deep
notch, leaving the right central and quadrate lobes
broadly confluent on the diaphragmatic surface of
the liver. The fundus of the gall bladder reaches
the diaphragmatic surface. The caudate lobe con-
sists almost entirely of a large papillary process.
Renvall's descriptions of the liver of Procyon lotor
and Nasua sp. agree with my observations in all
essential respects. Apparently the liver of Ailurus
is very similar to that of the Procyonidae (Carlsson,
1925, figs. 13-14).
In the Ursidae ( Ursus americanus and Helarctos
malayanus examined) the accessory lobes are rela-
tively small, the postcava is embedded in the cau-
date lobe, and the gall bladder is not visible from
the diaphragmatic surface. Renvall's description
and figure of the liver of Ursus arctos agree closely
with my observations. The liver of Ailuropoda
resembles in general that of the bears, but the ac-
cessory lobes are much reduced. The quadrate
lobe is a mere appendage of the right central lobe
and is visible only on the visceral surface. The
caudate lobe is smaller than in the bears, but still
partly embraces the postcava, and the papillary
and caudate processes are much reduced. The
gall bladder is invisible from the diaphragmatic
surface. In both bears and panda the liver is high-
domed and much flattened dorsoventrally, although
this merely reflects the shape of the cavity into
which the liver is molded.
Among vertebrates the liver is larger in carni-
vores and omnivores than in herbivores (Siwe,
1937; see also Table 18), and is relatively larger
in small mammals. Reliable data available to me
indicate that the weight of the liver in carnivores
is about 3-4 per cent of body weight (Table 18).
Unfortunately no reliable figures are available for
bears. The relative liver weight in Ailuropoda is
Table 18. LIVER WEIGHT IN MAMMALS
N
Canis familiaris 9 4
Canis lupu; cT 1
Potos flavus 9 1
Ailuropoda melanoleuca cf 1
Felis domestiea cf 52
Felis domestiea 9 52
Felis leo cf 2
Homo sapiens cf
Equiis caballus cf 5
Equus caballus 9 10
Bos taurus 9 218
Sus scrofa cf 53
Sus scrofa 9 36
Body weight
Liver weight
Liver weight
(gms.)
(gms.)
Body weight
Source
23,710
693
2.9
Crile and Quiring (1940)
29,940
925
3.1
Crile and Quiring (1940)
2,620
98.6
3.8
Crile and Quiring (1940)
60,000
1564
2.6
Original
2,822
101.5
3.6
Latimer (1942)
2,445
88.6
3.6
Latimer (1942)
190,800
5725
3.0
Crile and Quiring (1940)
160,000]
1500
2.5
Morris, Human anatomy
485,310
5685
1.2
Crile and Quiring (1940)
443,360
6176
1.4
Crile and Quiring (1940)
413,000
5747
1.4
Crile and Quiring (1940)
102,060
1488.3
1.4
Crile and Quiring (1940)
102,060
1547.3
1.5
Crile and Quiring (1940)
DAVIS: THE GIANT PANDA
215
Sphincter pylori
Duodenum (pars superior)
Valvula pylori
Ductus pancreaticus ace.
Papilla minor
Ductus
choledochus
Papilla major.
Ductus pancreaticus major
Fig. 116. Pancreatic and common bile ducts of Ailuropoda.
slightly less than in any other carnivore in Table 18,
but is much greater than in any of the herbivores.
VIII. PANCREAS AND SPLEEN
The pancreas (figs. Ill, 116) is a compact, V-
shaped structure embracing the stem of the com-
mon mesentery and the mesenteric blood vessels
between its arms. The lateral edge of the vertical
arm (caput pancreaticus) is in intimate contact
with the duodenum, while the other (corpus pan-
creaticus) is related to the greater omentum near
the pylorus. The two arms are nearly equal in
length, each measuring approximately 85 mm.
There is a well-defined processus uncinatus, which
is hooked around the anterior mesenteric blood
vessels.
The pancreas is drained by two ducts (fig. 116).
The more posterior of these appears to be homolo-
gous with the main pancreatic duct (Wirsung) be-
cause of its position and relation to the ductus
choledochus, although it is much less extensive and
of smaller caliber than the accessory duct (Santo-
rini). The main duct drains the lower end of the
head and the uncinate process. It arises in the
uncinate process, turns craniad into the head, and
then caudad at an acute angle, to enter the wall
of the duodenum; its course is thus more or less
S-shaped. It opens on the papilla major by an
independent outlet that is immediately caudad of
the outlet of the ductus choledochus. The acces-
sory duct arises in the tail of the pancreas and runs
along the corpus and into the anterior end of the
head. It opens into the duodenum about 18 mm.
craniad of the papilla major. There is no connec-
tion between the main and accessory ducts.
No taxonomically significant variation in the
gross structure of the pancreas has been demon-
strated for the Carnivora. In all it is a compact
organ, V-shaped or L-shaped (even circular, Carls-
son, 1925). Typically there are two ducts, al-
though one is suppressed in occasional individuals.
The main duct opens with the ductus choledochus,
the other farther caudad.
The spleen (lien) is a long narrow structure,
340 mm. in length and about 40 mm. in width,
that lies mostly along the caudal part of the greater
curvature of the stomach (fig. 111). It is slightly
wider anteriorly than posteriorly. It is also much
flattened, its thickness averaging only about 10
mm., so that it has only two surfaces, a gastric
216
FIELD lANA: ZOOLOGY MEMOIRS, VOLUME 3
and a diaphragmatic. The anterior end of the
spleen is bent to the right almost at a right angle,
so that it lies dorsad of the fundus of the stomach.
The posterior end is also bent to the right to follow
the sharp flexure of the stomach at the beginning
of the pylorus, which gives the whole spleen the
general form of a letter C. The organ is bound
rather closely to the stomach throughout its entire
length by the gastrolienal ligament, which attaches
to the gastric surface at the hilus and does not ex-
ceed 30 mm. in width. A narrow lienorenal liga-
ment, attaching to the edge of the spleen near its
middle, binds the spleen to the left kidney.
The spleen appears to vary little among the Car-
nivora. In all forms in which it has been described
or in which I have examined it (Canis,Bassariscus,
Procyon, Ursus, Felis) the spleen is a tongue-shaped
organ with an elongate hilus on the gastric surface.
It was relatively broader in the procyonids than
in the others.
IX. DISCUSSION OF DIGESTIVE
SYSTEM
If the operation of evolutionary mechanisms on
the skeleton and musculature is sometimes difficult
to interpret, the difficulty is multiplied when we
come to the digestive system. The masticatory
apparatus usually shows the most exquisite adap-
tive relations to diet, but the rest of the digestive
apparatus may or may not show differences corre-
lated with food habits. A horse, with a simple
stomach and intestine only 10 times body length,
does as well on a diet of grass as does a cow with
its complex stomach and intestine 25 times body
length. Yet among mammals there is in fact a
broad correlaton between diet and the structure
of the digestive system ; this correlation is with the
mechanical, rather than the chemical, properties
of the food (Flower, 1872; Pernkopf, 1937).
Since a higher taxonomic category is usually
characterized by a major adaptation, often to a
particular diet, we would expect the gut in the vast
majority of cases to be no more variable than other
taxonomic characters. The fact is that within the
family or order the gut tends to remain conserva-
tive even in the face of the most extreme changes
in diet. No better example of this conservatism
could be asked than the herbivorous carnivores.
For most features of the digestive system the clos-
est and most consistent correlation is with the
taxonomic unit, which exists even where no other
correlation can be demonstrated. It is strikingly
evident in the liver, where form is tremendously
varied but has no conceivable relation to function.
All attempts to correlate lobation of the mammal-
ian liver with ramification of the hepatic vessels
or bile ducts, or with posture or other mechanical
factors, have failed (Siwe, 1937). Yet lobes and
fissures are clearly homologous throughout the
Mammalia, and patterns characteristic of orders,
families, and genera are evident everywhere (Meyer,
1911).
Variation in the digestive system, then, is not
random, even where there is no obvious way that
selection can determine form. But it is evident that
evolution of the gut involves factors more subtle
than the mechanical and architectural require-
ments that largely determine the evolution of the
skeleton and skeletal musculature.
Among the arctoid carnivores, diet ranges from
practically exclusively carnivorous in such canids
as the coyote, through heavily herbivorous in the
bears, to exclusive foliage-eating in the giant panda.
These differences in diet are accompanied by cor-
responding modifications of the masticatory appa-
ratus, but the structure of the remainder of the
digestive system is astonishingly uniform through-
out this group.
The digestive system of the bears differs from
the more generalized carnivore condition in sev-
eral points, mostly relatively minor and adaptive
to a heavily herbivorous diet (but not necessarily
one composed of foliage) . Such adaptive features
are the large parotid gland, the numerous vallate
papillae, and the length of the intestine. Other
ursid features, not overtly adaptive, are the fre-
quently semicircular arrangement of the vallate
papillae, the paired pharyngeal bursae, the small
size of the accessory lobes of the liver, the presence
of a colic loop in the intestine, the absence of an
ileocolic valve, and the globular form of the py-
loric region of the stomach.
The digestive system of Ailuropoda agrees closely
with that of the Ursidae in most of these features.
Strikingly different is length of intestine; less ex-
treme are differences in the form of the stomach
and liver. The intestine is typically elongate in
herbivorous mammals, but there are many excep-
tions to this rule (Weber, 1928; Jacobshagen, 1937).
The exceptions can be only partly explained by
large caeca, expanded intestinal diameter, or the
tendency for primitive forms to have a short in-
testine regardless of diet. Secondary reduction of
intestinal length in connection with secondary her-
bivory, such as must have taken place in Ailuro-
poda and apparently in Ailurus, is something else.
A. B. Howell (1925) observed a similar relation in
comparing the digestive tract of a nut- and fruit-
eating tree squirrel (Sciurus carolinensis) with that
of a grass-eating ground squirrel {Citellus beldingi).
The small intestine was nearly twice as long in the
Sciurus as in the Citellus. Howell says "the sig-
DAVIS: THE GIANT PANDA
217
nificance of this discrepancy in length is not un-
derstood. It is at variance with what might be
expected."
Reduced intestinal length has been shown to be
correlated with a herbivorous diet in experimental
animals. Haesler (1930) divided a litter of nine
pigs into three groups, one of which was raised on
an exclusively carnivorous diet, one on an exclu-
sively herbivorous diet, and one on a mixed (nor-
mal) diet. At the end of the experiment, in the
animals on a herbivorous diet the stomach was
largest, the small intestine shortest and with the
smallest internal surface area, the caecum largest,
and the colon shortest but with the greatest inter-
nal surface area (Table 19). In the pigs on a car-
nivorous diet the stomach was smallest, the small
intestine longest but intermediate in surface area,
the caecum and colon were smallest. The length
differences in Table 19 are far smaller than the
differences of hundreds, even thousands, of per-
centage points in normally herbivorous versus nor-
mally carnivorous species of mammals. Wetzel
(1928) had earlier had similar results in a less care-
fully planned experiment on rats.
The data in Table 17 show that the total intes-
tine is relatively about half as long in Ailuropoda
as in the bears. The difference is due to a shorter
small intestine, since relative length of colon is
the same in the two groups. In both groups the
colon is longer than in any other for which we
have data. But whereas colon circumference in
our Ursus americanus is identical with mean small
intestine circumference (27.6 mm.), in Ailuropoda
the colon circumference (99) exceeds mean small
intestine circumference (90) by about 10 per cent.
Therefore the relative surface area of the colon is
about 10 per cent greater in Ailuropoda. Conse-
quently, both in Haesler's experimental animals
and in our Ailuropoda compared with Ursus, length
and surface area of small intestine are reduced, and
surface area of colon is increased, with an exclu-
sively herbivorous diet. The slight reduction in
colon length reported by Haesler was not evident
in our carnivore material.
Haesler concluded that the efficient factor deter-
mining differences in gut proportions in mammals
is the volume of the residue of ingesta that remains
insoluble after it has passed through the stomach
and small intestine. The more voluminous this is,
the larger are the caecum and colon, and vice
versa. Where the ingesta is soluble only after be-
ing acted upon by bacteria and protozoa in the
caecum and/or colon, the small intestine functions
largely to transmit the ingesta from stomach to
caecum colon. This is the case in Ailuropoda and
in Haesler's pigs reared on a herbivorous diet. In
Table 19. PERCENTAGE DIFFERENCES FROM
CONTROL ANIMALS IN GUT MEASUREMENTS
OF PIGS RAISED ON HERBIVOROUS AND CAR-
NIVOROUS DIETS
(Data from Haesler, 1930)
Internal
Diet Length Volume Surface
% %
cfu /Herbivorous ... + 6.9 ....
^'^'^h (carnivorous ... -10.3
^"J^',' ;. /Herbivorous -6.2 -17.6 -13.6
^"'^^^""^- \ Carnivorous +1.4 -8.1 -4.0
/-o, /Herbivorous ... +50.0 ....
C^^'^"'" (carnivorous ... -14.3
r^u^ /Herbivorous -2.4 +35.5 +17.3
^'" \ Carnivorous -12.4 -43.0 -28.0
T, J 1 n ,f /Herbivorous 5.3 + 7.0 4.0
^'^'''^"'^-- /Carnivorous -1.5 -19.3 -9.6
such cases the small intestine has little digestive
function, and reduced length is advantageous. In
ruminants, on the contrary, cellulose solution oc-
curs mainly in the rumen (Dukes, 1935), and the
small intestine can therefore function in digestion
and absorption, and length is advantageous.
In mammals that habitually ingest large quan-
tities of cellulose, either the stomach is complex or
there is a large caecum. Ailuropoda has neither,
and in this animal the normal ingesta must be
practically insoluble until it reaches the colon.
With no caecum, and a short and relatively nar-
row colon, digestion must be remarkably ineffi-
cient. Observers have commented on the high
proportion of undigested material in the feces of
Ailuropoda (p. 27).
The stomach of Ailuropoda differs from that of
Ursus chiefly in the extensive development of the
pyloric region. In the panda this region is almost
gizzard-like. The stomach in Howell's squirrels
agreed with conditions in the panda; in the grass-
eating Citellus the pylorus was more tubular and
more muscular than in Sciurus. Kneading, mix-
ing, and soaking are prerequisite to cellulose di-
gestion (Dukes, 1935), and in simple stomachs the
pylorus is the site of true motor activity (Pern-
kopf, 1937). Thus the modified pyloric region in
Ailuropoda appears to perform the kneading func-
tion and therefore to be directly adaptive.
The liver is consistently smaller in typically her-
bivorous than in typically carnivorous mammals,
and it appears to be slightly smaller in Ailuropoda
than in other carnivores. Since protein break-
down and the emulsification, digestion, and ab-
sorption of fats are the primary digestive functions
of the liver, it is scarcely surprising that this organ
is smaller in herbivorous mammals whose diet has
a high foliage content. In the Carnivora the ac-
cessory lobes appear to be affected first when there
218
FIELD lANA: ZOOLOGY MEMOIRS, VOLUME 3
is phylogenetic reduction of liver size, and this may
explain the much reduced accessory lobes in Ailu-
ropoda as compared with the bears and other arc-
toid carnivores. Since the liver is a passive organ,
molded by surrounding organs, we would expect
the form of the liver in Ailuropoda to reflect the
somewhat modified stomach form.
Nothing is known of the morphogenetic mech-
anisms controlling growth and differentiation of
the digestive system. Experiments such as those
of Haesler indicate a certain capacity for individ-
ual adaptation in the proportions of the gut, but
the differences fall far short of those seen in species
adapted to extremes of herbivorous or carnivorous
diet. Thus selection, operating through genetic
mechanisms, must be at least partly responsible
for differences in the digestive system such as those
seen in Ailuropoda as compared with the bears.
X. CONCLUSIONS
1. The gross morphology of the digestive sys-
tem of the Ursidae differs in details from that of
other arctoid carnivores. Most of these differ-
ences represent adaptations to a heavily herbivo-
rous diet, but a few conspicuous differences are not
overtly adaptive.
2. The digestive system of Ailuropoda agrees
closely with that of the Ursidae in nearly all de-
tails. It differs in the pyloric region of the stom-
ach, in liver form, and in intestinal proportions.
3. The pylorus is almost gizzard-like in Ailu-
ropoda, an adaptation for kneading and mixing
the ingesta.
4. The liver is small and the accessory lobes
are much reduced. In mammals a small liver is
correlated with a herbivorous diet.
5. Length and internal surface area of the small
intestine are much reduced in Ailuropoda as com-
pared with the bears. The normal ingesta of Ailu-
ropoda is probably still insoluble in this part of
the gut.
6. Surface area of the colon, the gut region
where solubility of fibrous ingesta would be great-
est, is greater in Ailuropoda than in the bears.
7. Thus all significant differences in gross struc-
ture between the gut of Ailuropoda and the gut of
the Ursidae are directly adaptive to the bulky
fibrous diet of the panda.
8. The genetic mechanisms controlling growth
and differentiation of the elements of the digestive
system are unknown. Consequently nothing is
known of the morphogenetic mechanisms whereby
adaptive changes in the gut can be effected.
UROGENITAL SYSTEM
I. URINARY ORGANS
A. Kidneys
The kidneys are situated with their anterior bor-
ders about on a level with the anterior border of
the first lumbar vertebra; their long axes converge
slightly anteriorly. The anterior border of the
right kidney is 15 mm. farther craniad than that
of the left. The kidneys weigh 93 and 87 gi-ams,
together 180 grams. This represents a ratio to
body weight of 1 : 333. The dimensions in milli-
meters are as follows (measurements in parenthe-
ses are from an adult female as given by Raven) :
Length
Right 105(112)
Left 100(108)
Width Thickness
51 (62) 33 (26)
55 (55) 31 (25)
Each kidney (fig. 135) is composed of several in-
dependent lobes or "renculi." The renculi are
packed closely together, and the organ as a whole
has the usual kidney form. The entire kidney is
enclosed in a thin tight-fitting capsule whose walls
contain a quantity of fat, and each renculus in turn
has an individual capsule of its own. The right
kidney is composed of 10 renculi, 5 of which are
double, giving a total of 15. The left kidney is
made up of 10 renculi, 8 of which are double, for
a total of 18. A single layer of the capsular mem-
brane separates the halves of the double renculi.
The renculi are arranged around a prominent renal
fossa.
The renculi average about 20 mm. in diameter.
Each is composed of a heavy cortex, about 6 mm.
thick, surrounding a small medulla averaging 7.1
mm. thick. The difference between cortex and
medulla is not well marked macroscopically, and
the inner and outer zones of the medulla cannot
be distinguished. The medulla is composed of
from one to three pyramids, each of whose apices
forms a very long (4 mm.) and prominent papilla.
Many renculi have three papillae. There is a total
of 23 papillae in the right kidney. Under a hand
lens the numerous foramina papillaris, the termi-
nations of the papillary ducts, can be seen on the
papillae.
All the papillae of a single renculus lie together
in a common minor calyx. The minor calyces of
the several renculi unite, within the renal fossa,
into two major calyces, an anterior and a poste-
rior. The two major calyces unite outside the
fossa to form the slightly expanded proximal end
of the ureter. There is no renal pelvis.
The literature on the structure of the carnivore
kidney has been reviewed by Gerhardt (1914),
Sperber (1944), and Schiebler (1959). The com-
parative anatomy of the ursid kidney was described
by Guzsal (1960). In all fissiped carnivores, ex-
cept the Ursidae and Lutrinae, the kidney is sim-
ple, with a single papilla or a crest. The simple
kidney with a single papilla is the most primitive
type of mammalian kidney, and a crest is a slightly
modified papilla (Sperber). In the Ursidae (and
Lutrinae) the kidney is renculate, the most highly
modified kidney type known among the Mam-
malia. In the Ursidae each kidney is composed
of 23 34 renculi, except Thalarctos, in which there
are twice as many (Table 20). Usually a few ren-
culi are double, in one case even triple. Each
renculus has a papilla; when a renculus is double
there are two papillae, so the number of papillae
is probably an index of the number of units com-
posing the kidney.
Since many of the renculi have three papillae in
Ailuropoda, the total number of papillae is about
the same as in the bears, although the number of
renculi is considerably less. From what is known
of the ontogeny and comparative anatomy of the
mammalian kidney, it is evident that the multi-
papillate renculus type of the panda represents a
partial consolidation of the unipapillate renculus
type of the ursids, a partial "reversion," so to speak,
to the simple kidney type from which the renculate
kidney was originally derived.
Among mammals renculate kidneys are associ-
ated with large organism size and, /or aquatic habits.
Factors in addition to organism size must be in-
volved among terrestrial mammals, for the kidneys
are simple (although modified in other ways) in as
large a mammal as the horse, and among terres-
trial carnivores they are renculate in all bears re-
gardless of size, but simple even in the largest of
the cats. Dividing the kidney up into renculi re-
duces nephron length. The factor limiting nephron
length is the pressure required to force fluid through
219
220
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Table 20 NUMBER OF RENCULI COMPOSING KIDNEY IN BEARS
Renculi
No.
Ursus arctos 34
Ursus arctos 33
Ursus americanus 28
Ursus tibelanus 22-25
Thalarctos 62-65
Melursus 23
Melursus 26-30
Helarclos 23
Ailuropoda 10
renculi
Renculi
No.
Total
Source
34
Sperber (1944)
(1 triple)
37
Guzsal (1960)
3
31
Guzsal (1960)
1
22-26
Guzsal (1960)
several
65 +
Guzsal (1960)
4
27
Gerhardt (1914)
7
26-30
Guzsal (1960)
7
23
Original
5-8
15-18
Original
the nephron (Sperber). Relative thickness of cor-
tex and medulla, particularly of the medulla, is
reduced in renculate kidneys. Table 21, based on
Sperber, gives the absolute and relative dimen-
sions of cortex and medulla in representative arc-
toid carnivores. Sperber's data show that relative
thickness of cortex and medulla (particularly me-
dulla) is greatest in the most primitive kidney
types, least in the most highly modified. The fig-
ures for carnivores given in Table 21 conform to
Sperber's general figures for each kidney type in
the Mammalia.
Relative kidney size varies with organism size,
the kidneys being relatively larger in small mam-
mals than in large mammals. Beyond this, how-
ever, the kidneys are relatively heavier in flesh-
eating than in plant-eating mammals (Table 22).
In the bears and giant panda the ratio is like that
of herbivores rather than like that of other car-
nivores.
Thus it appears that in Ailuropoda the kidney is
basically of the ursid type, but that it has begun
to revert to a simpler type. The significance of
this reversion is not apparent, although there are
indications of "fetalization" in other structures in
this region the postcava and external genitalia, for
example. It is probably a part of the general dis-
turbance in the lumbosacral region of Ailuropoda.
B. Ureters
The right ureter is 195 mm. in length and 4 mm.
in diameter; the left is slightly shorter. The ure-
ters are separated by a distance of 95 mm. at their
origins, and converge toward the bladder across
the psoas muscles. Near the bladder they pass
between the external iliac and hypogastric vessels.
The ureters enter the dorsal wall of the bladder
at an oblique angle near the neck. The two ure-
ters penetrate the bladder 20 mm. apart.
C. Bladder
The empty bladder (fig. 118) is an elongate pear-
shaped sac, much flattened dorsoventrally. The
entire organ lies anterior to the very short symphy-
sis pelvis. The bladder measures 105 mm. in length
and 55 mm. in width. The walls are 9 mm. thick.
The lining of the bladder is thrown up into irreg-
ular longitudinal folds, except for the area occu-
pied by the trigone. The openings of the ureters
appear as a pair of dimple-like depressions, 25 mm.
apart. The trigonum vesicae is a prominent
elongated triangle; the uvula vesicae is present
as a faint longitudinal elevation along its mid line
Table 21. DIMENSIONS AND PROPORTIONS OF KIDNEYS IN ARCTOID CARNIVORES
Thickness
(in mm.) of Layer thickness X 10
kidney layers kidney size
Kidney Cortex +
size* Cortex Medulla medulla Cortex Medulla Source
... , [57 ... ... ... ... ... Raven (1936)
Ailuropoda .^ -g g^ ^j 2.3 1.0 1.3 Original
Ursus arctos 65 4.0-4.5 8.5 1.9 .6 1.3 Sperber (1944)
Helarctos malayanus 60 5.2 6.9 2.0 .9 1.1 Original
D ,, / 30 6.3 12.5 6.2 2.1 4.1 Original
Procyonlolor | gS 5.5 10.5 5.7 1.9 3.8 Sperber (1944)
Nasuanarica 26 5.5 10.0 6.0 2.1 3.9 Sperber (1944)
Canis familiaris 40 7.0 17.0 6.0 1.7 4.3 Sperber (1944)
Canislupus 51 7.0 23.0 5.9 1.4 4.5 Sperber (1944)
* The cube root of the product of the three dimensions of the kidney.
Cants familiaris 9
Canis lupus cf
Ailuropoda cf
Ursus horribilis 9
Procyon lotor 9
Felis domeslica < ^
Felis leo cf
Homo sapiens cf
Equus caballus I ^
Bos taurus 9
Sus scrofa < g
DAVIS: THE GIANT PANDA
Table 22. KIDNEY WEIGHTS IN MAMMALS
221
Body weight
Kidney weight
Kidney weight
N
(gms.)
(gms.)
Body weight
Source
23,710
152
.64
Crile and Quiring (1940)
29,940
223
.74
Crile and Quiring (1940)
60,000
180
.30
Original
142,880
548
.38
Crile and Quiring (1940)
4,536
37
.82
Crile and Quiring (1940)
52
52
2,822
2,445
21.1
16.9
.74
.69
Latimer (1939)
Latimer (1939)
2
190,800
1610
.84
Crile and Quiring (1940)
168
.59
Morris, Human Anatomy
10
5
443,360
485,310
1667
1972
.38
.41
Crile and Quiring (1940)
Crile and Quiring (1940)
!18
413,000
983
.24
Crile and Quiring (1940)
53
36
102,060
102,060
238
264
.23
.26
Crile and Quiring (1940)
Crile and Quiring (1940)
Ligaments of the Bladder
The bladder is supported by the usual two sets
of ligaments, the "false" ligaments and the "true"
ligaments.
The false ligaments are composed of dorsal and
ventral elements. A long continuous fold of peri-
toneum is attached to the dorsum of the bladder.
Medially it forms a deep triangular cul-de-sac,
roofed over with peritoneum through which the
ductus deferentes run. From this fold of perito-
neum dorsal and lateral ligaments run to the walls
of the pelvic cavity. A single ventral fold of peri-
toneum runs from the venter of the bladder to the
ventral abdominal wall. The urachus arises be-
hind the ventral ligament and runs craniad on the
belly wall to the umbilicus.
There are three true ligaments from the poste-
rior part of the bladder: the unpaired puboprostatic
ligament running from the ventral midline of the
neck of the bladder to the pubis, and the pair of
lateral ligaments running from the lower part of
the bladder to the walls of the pelvis.
II. MALE REPRODUCTIVE ORGANS
A. Male Perineal Region
The perineal region (fig. 117) comprises the anus,
the prepuce, and the naked glandular region lying
between them. The testes lie immediately caudad
of the inguinal canal, which places their caudal
borders about on a line with the caudal end of the
symphysis pelvis. This means that the caudal end
of the testis lies about 35 mm. in front of the penis
and 50 mm. laterad of the midline, which places
them at a considerable distance from the perineum.
In addition, there is no scrotum or other external
evidence of the site of the testes in the juvenile
individual dissected. At sexual maturity the tes-
ticles are very evident.
The anus is a transverse aperture, somewhat
U-shaped, with the concavity directed ventrally.
It is 30 mm. wide in the contracted condition, and
is surrounded by an extensive area of light-colored
naked skin. This hairless area is triangular in out-
line, with the base of the triangle at the root of the
tail and the apex continued ventrad to the prepuce.
It is granular in texture, the granulations becom-
ing less pronounced ventrally as the prepuce is
approached. The dorsal wall of the anus forms a
prominent cushion, underlain by fat, which is tra-
versed by deep furrows radiating from the anus.
Typical anal glands are absent.
Ventrad of the anus is a narrow vertical median
prominence bounded laterally by a deep furrow on
each side, which extends from the anus to the dor-
sal root of the prepuce. It widens slightly toward
the anus, into which it is continued, and shows a
faint median raphe.
The structure of the external genitalia is remark-
able. The penis is entirely withdrawn within a
prominent heart-shaped elevation. This eleva-
tion, which represents the prepuce, measures about
40 mm. in both transverse and longitudinal diam-
eters. It is sharply constricted off from the sur-
rounding skin by a shallow furrow laterally and a
deep excavation dorsally, which gives it a button-
like appearance. There is an additional concen-
tric furrow on its surface on either side. Its outer
surface is rather well haired, except dorsally, where
the naked area is continuous with the naked area
of the perineum. An aperture, around which the
skin is puckered, occupies the center of the promi-
nence. A faint median raphe extends dorsad from
the aperture.
The lining of the prepuce is heavily pigmented
and has a puckered, honeycomb appearance. It
is reflected to form the covering of the pars intra-
praeputialis of the penis. Thus the pars intraprae-
putialis appears to be enclosed in a thick-walled
pocket, the lining of which would form the outer
covering of the body of the penis during erection.
222
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Fig. 117. Perineal region of subadult male Ailuropoda (Su Lin).
Dorsally (posteriorly) the lining of the prepuce is
attached to the pars intrapraeputialis by a small
but conspicuous frenulum.
B. Testis and Its Appendages
The testes lie just outside the external inguinal
ring, and hence are prepenial in position (fig. 135).
The two organs are separated by a distance of
70 mm. There is no true scrotum, and at least in
the subadult animal dissected the testes and their
wrappings are so embedded in fat that they do not
even produce a swelling in the contom- of the body.
The testis is an ovate structure, 28 mm. in
length, and wider posteriorly than anteriorly. It
is considerably flattened dorsoventrally.
The epididymis is relatively large, and is di-
vided into three well-marked regions: caput, cor-
pus, and Cauda. The caput is a relatively small
expansion occupjnng the usual i>osition over the
anterior end of the testis. The corpus is a flat
Ureter
Vesica urinaria
Gl. ductus deferenti
M. ischiocavernosus
Papilla ductus deferenti
M. bulbocavemosus
Fascia penis
M. retractor penis
Testis
Fig. 118. Male reproductive organs of Ailuropoda.
223
224
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
M. ischiocav
M. bulbocavernosus
M. sphincter
Caput penis
fibrusum
M. sphincter urethrae
membranaceae
M. bulbocavernosus
Bulbus urethrae W/W'^/^
W
penis
Corpus ca%'ernosui
Praeputium (cut)
M. sphincter urethrae
membranaceae
. ^.., '-J,--- P^f^ membranaceae
,/^^^*=s4S__urethrae
Corpus spongiosum-^ W
Corpus fibrosum
Tunica albuginea
Pars cavernosa urethrae
Bacuhim
Praeputium (cut)
Fig. 119. Penis of Ailuropoda. A, lateral aspect, B, longitudinal section.
band, 8 mm. wide, closely applied to the lateral
border of the testis. The cauda is by far the larg-
est region of the epididymis. It is a conical caplike
structure over the posterior end of the testis.
The ductus deferens (fig. 118) is continued
from the tail of the epididymis along the medial
border of the testis, entering the funiculus sper-
maticus at the anterior end of the testis. The
funicular part of the ductus is about 80 mm. long.
At the entrance to the inguinal canal it leaves the
spermatic vessels and loops back, ventrad of the
terminal vessels of the aorta and the ureter, to the
dorsiun of the bladder. The last 45 mm. of the
ductus, Ijnng on the neck of the bladder, is en-
larged and encased in a thick layer of glandular
tissue. The ducts from each side, which are con-
siderably enlarged by their glandular investment,
approach each other on the neck of the bladder.
They unite, 5 mm. before reaching the wall of the
urethra, into a common duct, which passes through
the wall of the urethra at a very oblique angle.
The duct opens into the urethral canal on a small,
elongate papilla.
There is no indication of vesicular, prostate, or
bulbo-urethral (Cowper's) glands.
The urethra is divisible into pars membranacea
and pars cavernosa. The pars membranacea is
60 mm. in length, with heavy muscular walls about
4 mm. thick. The lining of the lumen is thrown
up into prominent longitudinal ridges at its prox-
imal end. The pars cavernosa is 43 mm. in length.
The lining of its lumen is elevated into numerous
small longitudinal mucous folds, and the lining of
the distal half, except near the external orifice, is
irregularly pigmented. There is a prominent longi-
tudinal fold along the dorsal wall of the fossa nav-
icularis.
C. Penis
The penis (figs. 118, 119, 135) is remarkable for
its small size. It measures only 36 mm. in length
(measured from the posterior border of the ischio-
cavernosus muscle) by 13 mm. in diameter. The
corresponding measurements on the penis of a fully
adult male (Mei Lan) are 70 mm. by 25 mm. The
organ is divided into a button-like pars intraprae-
putialis and a cylindrical body. The penis is S-
shaped, its tip directed posteriorly. The prepuce
was described on page 221.
In addition to its crural attachment to the ischia,
the penis is supported by a pair of suspensory liga-
ments arising from the ischiadic part of the sym-
physis pelvis. These ligaments attach to the sides
of the penis at its base, where the ischiocavernosus,
sphincter ani externus, and suspensory ligament
have a common attachment. There is also a paired
M. retractor penis (p. 172) inserting into the base
of the pars intrapraeputialis.
The body or shaft of the penis is composed prin-
cipally of three cavernous elements, the two cor-
pora fibrosa and the corpus spongiosum. These
are enclosed within a common sheath of tough
connective tissue, the fascia penis.
The two corpora fibrosa (BNA: corpora caver-
nosa penis) are remarkably small, each scarcely
exceeding the corpus spongiosimi in size. The
corpus fibrosum arises, as the crus penis, from the
descending ramus of the ischium, covered by the
ischiocavernosus muscle. The two corpora con-
verge to form the body of the penis. Anteriorly
they are continued as the baculum, which is lodged
in the distal part of the penis but does not extend
into the pars intrapraeputialis. Each corpus is
enclosed in a tough tunica albuginea, and between
DAVIS: THE GIANT PANDA
225
the two corpora these are united into a median
septum penis.
The corpus fibrosum is composed of dense spongy
tissue, divided into two regions differing sharply in
structure (fig. 119). The basal part (correspond-
ing to the unossified part of the corpus fibrosum
in bears and procyonids) is a firm meshwork with
coarse interspaces, resembling the corpus fibrosum
of other arctoid carnivores. Between this basal
part and the baculum (corresponding to the prox-
imal part of the baculum in bears and procyonids),
the meshwork contains an immense number of
glistening white fibers, straight and radially ar-
ranged. The medial ends of these fibers are deeply
embedded in the tunica albuginea. To judge from
its position, this part of the corpus fibrosum repre-
sents the degenerate proximal part of a formerly
much longer baculum.
The corpus spongiosum (BNA: corpus caver-
nosum urethrae) surrounds the pars cavernosa ure-
thrae, except distally where it is replaced by the
corpus cavernosum. It begins proximally as a rela-
tively small bulbus urethrae, which tapers gradu-
ally into the corpus. The bulbus is surrounded by
a small M. bulbocavernosus.
The pars intrapraeputialis is the hemispher-
ical tip of the penis lying within the preputial cav-
ity. It is broader transversely than dorsoventrally,
and is composed of a caput and a collum marked
off from the head by a faint constriction. The in-
tegument covering the head is continuous with the
integument lining the preputial cavity. It is faintly
pitted, and is pigmented peripherally, unpigmented
centrally. A very small frenulum connects the
urethral border of the head with the prepuce. The
meatus of the urethra is a vertical slit in the center
of the head.
The interior of the pars intrapraeputialis and
the distal part of the body of the penis are filled
with erectile tissue, the corpus cavernosum.
This is exceedingly fine-meshed cavernous tissue,
clearly distinguishable from the coarser tissue of
the corpus spongiosum.
D. Baculum'
The baculum is a small, remarkably shaped
structure, completely different from that of any
other carnivore for which this bone has been de-
scribed (fig. 120). It is only 24 mm. in length.
There is a short, rod-like body from which rounded
winglike expansions, deflected downward at an an-
gle of about 45, arise. These wings occupy more
than the distal half of the bone. They are heavy,
with slightly irregular rounded edges, and the max-
Description from an adult male (CNHM 31128). The
baculum of the specimen dissected was incompletely ossified.
imum width across them is 12 mm. The tip of the
bone is a short, rounded, papilla-like projection.
The dorsal border of the baculum forms a rounded
keel. It is slightly sinuous in profile, convex over
the rodlike base and concave over the winglike
processes. The tip is directed slightly downward.
The wings form a deep inverted trough for the
urethra ventrally.
III. FEMALE REPRODUCTIVE ORGANS
The female reproductive organs are known only
from the description, based on the viscera of an
adult individual, given by Raven (1936). The fol-
lowing account is taken from his report (fig. 121).
The ovary is slightly flattened, rounded, and its
surface is fissured and pitted, thus having some-
what the appearance on the surface of a highly
convoluted brain. It measures 30 mm. in length
by 23 mm. in width and 11 mm. in thickness.
The uterine tube is very much contorted but
when straightened out measures 95 mm.
The corpus uterus is less than half the length
of the cornua and is slightly depressed. The cor-
nua are rounded on the free edge and diminish in
thickness toward the broad ligament. The surface
of the uterine mucosa is arranged in a mosaic with
distinct clefts separating the smooth areas making
up its surface. The mucosa has the same appear-
ance over its entire surface from the extremities of
the cornua to the cervix. The cervix is strong,
with comparatively muscular walls.
The vagina, which has a total length of 85 mm.,
is narrow, with firm muscular walls. Its mucosa
forms a series of closely set, transverse circular
folds. Caudally the vagina is bounded ventrally
by the tubercle, on the center of which is the ure-
thral opening, laterally and dorsally by the hymen,
which is a fold 8 mm. long.
The urogenital sinus, like the vagina and cor-
pus uterus, is flattened so that, though not wide, it
is more extensive transversely than dorsoventrally.
Of the specimen under consideration there is
preserved only a very little of the skin surround-
ing the genital and anal openings. It is bare, ex-
cept for a few hairs. On this skin are the openings
of numerous glands, which when squeezed express
an oily substance.
Lateral to the dorsal limit of the genital opening
on each side is a rather large crypt, which contains
the minute openings of many of these glands.
IV. DISCUSSION OF REPRODUCTIVE
ORGANS
The female reproductive organs in the arctoid
Carnivora show little variation in gross structure
226
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Ailuropoda melanoleuca
(3i
Ailunis fulgens
Bassarisctis astutus
t\?X'iir-^.~yyt''7,'j^.: ;^^ ... ^-^ .
Procyon lotor
Ursus atnericanus
Fig. 120. Baculum of Ailuropoda and other arctoid carnivores. A, dorsal, B, ventral, C, anterior views. Ailuropoda
X 2, others XI).
and therefore need not concern us further here.
The male organs, on the contrary, show extensive
and fundamental differences, both in the accessory
sex glands and in the copulatory organ.
The accessory sex glands of the Mammalia were
reviewed by Oudemans (1892), who recognized four
kinds of glands, and by Disselhorst (1904). With-
in the Carnivora there are pronounced differences
in the degree of development of these several kinds
of glands, and these differences are strictly corre-
lated with taxonomic units. No recent or detailed
studies exist for the accessory sex glands of the
Ursidae or Procyonidae. Owen says: "In the Bear
the sperm-ducts are enlarged and in close contact
at their terminations, with thick follicular walls"
[= glands of ductus deferens]; "beyond this gland-
ular part they retain their width, but contract to
open upon the verumontanum. A thin layer of
prostatic substance surrounds the beginning of the
urethra." He further states that in the Procyoni-
DAVIS: THE GIANT PANDA
227
dae and Mustelidae "the prostate is better devel-
oped than in the Ursines, especially in the Racoon,
in which it is in advance of the neck of the blad-
der." In Nasua sp. "the walls of the vasa defer-
Ailurus fulgens differs somewhat from Procyon
and Nasua, and is considerably different from Ur-
sus and Ailuropoda. In an adult male dissected
by me the distal ends of the ductus deferentes
Lig. ovarii proprium
Ovarium dext.
Mesosalpinx
Vestibulum vaginae
Clitoris-
FiG. 121. Female reproductive organs of Ailuropoda. Dorsal view, vestibule and vagina opened along mid-dorsal line
and spread out. (From Raven, redrawn).
entia are swollen immediately before these vessels were not dilated, there were neither glands of the
enter the urethra, and the prostate has a more ductus deferens nor ampullae, and the prostate
sudden projection at its upper end than I have ob- was present but much smaller and less sharply set
served in the musteline animals that I have dis- off from the urethra than in Procyon. This agrees
sected." (Turner, 1849.) essentially with Flower (1870).
In a specimen of Procyon lotor dissected by me The differences in the male accessory sex glands
the prostate was a large and prominent globular among the Carnivora, are:
structure surrounding the urethra at the base of vesicular glands absent all Carnivora
the bladder. The distal ends of the ductus defer- ^.^^^^^.^ ^1^^^^ ^^^^^^ Arctoidea
entes were dilated as in Ailuropoda, but these dila- Prostate large, glands of ductus deferens absent.
tions contained no glandular tissue. Instead this Ampulla ductus deferens small or ab.sent Canidae
portion of the ductus formed an ampulla with Ampulla ductus deferens large Procyonidae
thick cavernous walls, somewhat similar to the Prostate vestigial, glands of ductus deferens present,
, , ,oN 1 i i. fillmg ampulla Ursidae
ampulla of man. Weber (1928) erroneously states ^ , , ^ . >
^, f . . _, ., ^, ... i.- 1 Cowper s glands present I
that m the Procyonidae the prostate is vestigial Prostate present 1- Aeluroidea
and glands of the ductus deferens are present. Glands of ductus deferens absent J
228
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
This table is based largely on the data compiled
by Oudemans.
It is evident that Ailuropoda agrees closely with
the Ursidae in the structure of the male accessory
sex glands, and therefore these structures need not
be considered further here. Ailurus most closely
resembles the Procyonidae, but does not agree fully
with any other arctoid carnivore.
For the external genitalia the picture is not so
clear. The morphology of the penis was reviewed
by Gerhardt (1909, 1933), Pohl (1928), and Slijper
(1938). In the arctoid carnivores the penis is char-
acterized by the abdominal position of the prepuce
with the shaft long and enclosed in the belly skin
(Pocock, 1921), and by the great length of the
baculum and sparsity of erectile tissue (Gerhardt,
1933). In the Ursidae and Procyonidae the bacu-
lum extends proximally through the entire corpus
nearly to the root of the penis, and the corpus fibro-
sum, which continues proximally from the bacu-
lum, is correspondingly short. Except for the
intrapreputial part, the bone is clothed only in a
thin layer of fascia. The erectile tissue the cor-
pus cavernosum surrounding the intrepreputial
part of the baculum, and the corpus spongiosum
surrounding the urethra is remarkable for its
flabbiness, with delicate trabeculae enclosing huge
cavities.'
The ursid-procyonid-mustelid penis type is a
highly specialized derivative of the more primitive
vascular type, with the originally vascular corpora
fibrosa almost completely replaced by bone. This
might be called the "osseous type." As in the
likewise highly specialized fibro-elastic type of the
artiodactyls, temporary stiffening by engorgement
of the corpora fibrosa with blood has been re-
placed by permanent stiffening through special
supporting tissue.
The penis of Ailuropoda and Ailurus contrasts
sharply with the osseous type so characteristic of
all other arctoid carnivores. In the two pandas
this organ closely resembles the much more prim-
itive penis of the cats and certain viverrids: it is
small, posteriorly directed, sub-anal in position,
the corpus consisting largely of cavernous tissue,
the baculum absolutely and relatively small. From
the ontogenetic standpoint this approaches the fetal
condition, and represents a state of arrested develop-
ment, of "fetalization."
' It is remarkable that there are no descriptions of the
penis of any bear or any procyonid. I have dissected this
structure in a specimen of Procyon lotor, but no bear material
was available to me.
Since Ailuropoda is an ursid, it must originally
have had the highly specialized osseous penis type
of the bears. The remarkable structure of the
corpus fibrosum strongly supports this conclusion.
The antecedents of Ailurus are unknown, but cer-
tainly they were not ursids, and therefore fetaliza-
tion of its male external genitalia was independent
of the corresponding process in Ailuropoda. Fetali-
zation of the genitalia can scarcely be interpreted
as adaptive, and if not adaptive it must be associ-
ated morphogenetically with some other feature
that is adaptive. In Ailuropoda there is abundant
evidence of disturbance in the whole lumbosacral-
pelvic region, apparently associated with strong
cephalization of the body axis, and the modified
external genitalia may simply reflect this general
disturbance. There is no overt indication of
such disturbance in Ailurus. The only obvious
adaptive feature the two pandas have in common
is hypertrophy of the masticatory apparatus, and
it is difficult (though not impossible) to associate
this with fetalization of the male genitalia.
V. CONCLUSIONS
1. The kidney of Ailuropoda is renculate as in
the Ursidae, but the renculi are fewer in number
and are multipapillate.
2. The total number of renal papillae is about
the same as in bears. This suggests that each ren-
culus in Ailuropoda represents a consolidation of
several unipapillate renculi of the ursid type.
3. The male reproductive organs of Ailuropoda
may be divided into two parts:
(a) The accessory sex glands, which agree closely
with the distinctive pattern of the Ursidae.
(b) The external genitalia, which differ from
those of all other arctoid carnivores except
Ailurus.
4. The Arctoidea (except the Canidae) are char-
acterized by a highly specialized osseous penis, in
which erectile tissue has been almost completely
replaced by bone, and during erection the organ
increases only insignificantly in length and diam-
eter. The penis of the Canidae is unique among
mammals.
5. In Ailuropoda and Ailurus the penis has
been arrested at a much more primitive state of
development than in other arctoids. The signifi-
cance of this convergent "fetalization" of the ex-
ternal genitalia in two remotely related forms is
unknown. In Ailuropoda it may be associated
with cephalization of the body axis.
RESPIRATORY SYSTEM
I. LARYNX
The epiglottis(figs.l09,122) is triangular, with a
pointed apex and moderately large rounded wings.
The structure is nearly as broad as long. The epi-
glottis is subpalatal, not retrovelar, in position,
the tip lying below and well forward of the poste-
rior margin of the soft palate. A median glosso-
epiglottic fold connects the epiglottis with the base
of the tongue, and a very high and narrow pharyn-
goepiglottic fold runs laterally and slightly ante-
riorly from the side of the epiglottis to the wall of
the pharynx. The pharyngoepiglottic fold sepa-
rates a shallow epiglottic depression anteriorly
from an extremely deep and roomy pyriform re-
cess posteriorly. The pyriform recess abuts pos-
teriorly against the arytenoid and the arch of the
cricoid. Its floor is far below the inferior wall of
the esophagus.
A. Cavity of the Larynx
The laryngeal cavity is characterized by a very
deep vestibulum, the portion of the cavity lying
above the vocal folds (fig. 110). The superior
laryngeal aperture (fig. 122) is bounded by the
epiglottis anteriorly, followed by a short ary-epi-
glottic fold extending between the epiglottis and
the cuneiform cartilage. Behind the cuneiform
tubercle the aperture is bounded by the cuneiform
and arytenoid cartilages. The outlines of the cu-
neiform cartilage lying beneath the mucous mem-
brane are clearly visible. The cuneiform tubercle
is a conspicuous knob-like elevation formed by the
protruding upper end of the cuneiform cartilage.
The corniculate tubercle, lying behind the cunei-
form tubercle, is a less prominent elevation formed
by the corniculate process of the arytenoid.
The ventricular folds lie deep within the cavity
of the larynx. Each fold is a heavy, smoothly
rounded elevation in the laryngeal wall, broader
posteriorly than anteriorly and extending diago-
nally forward and downward from the cuneiform
cartilage to the anterior end of the laryngeal cav-
ity. The vocal lips lie several millimeters below
the ventricular folds and are much more promi-
nent. They stand nearer the median line than the
ventricular folds. The vocal lip is triangular in
cross section. Its thin free border is the vocal fold,
or true vocal cord. Between the ventricular and
the vocal fold is a shallow recess, the laryngeal ven-
tricle, running the length of the folds and broadly
open to the laryngeal cavity. There are no laryn-
geal sacs. The true cavity of the larynx, the space
below the vocal folds, is shallow and scarcely wider
than the rima glottidis anteriorly, gradually broad-
ening to the diameter of the larynx posteriorly.
B. Cartilages of the Larynx
Figure 123
The laryngeal skeleton is boxy. The margins of
the thyroid and cricoid cartilages are only slightly
excised, and the thyrohyoid and thyrocricoid mem-
branes correspondingly limited. The result is that
almost the entire laryngeal cavity is encased in
cartilage.
The thyroid cartilage is characterized by broad
lamina. The anterior thyroid notch is scarcely
indicated, but the posterior thyroid notch is deep,
extending more than half way to the anterior mar-
gin of the cartilage. The dorsal outline of the
cartilage is nearly straight. The anterior and pos-
terior cornua are relatively short and stout, and
about equal in length. There is a poorly defined
muscular process near the middle of the posterior
margin, and from this a faint linea obliqua extends
anteriorly and dorsally across the lamina. Above
the muscular process, the posterior margin is deeply
excavated to form a pit for muscle attachment.
The cricoid cartilage is completely divided at
the ventral midline, the two halves of the arch
separated by an interval of about 2 mm. There
is in addition a deep U-shaped notch in the poste-
rior margin at the ventral midline and a shallower
notch in the anterior margin. The arch is concave
in cross section, and is otherwise practically de-
void of surface relief. The lamina is about twice
as broad anteroposteriorly as the arch, and is quad-
rangular in outline, somewhat longer than broad.
Its anterior margin has a shallow U-shaped notch
at the midline. There is a prominent median keel
separating the areas of origin of the two posterior
cricoarytenoid muscles. The cricothyroid articu-
lation is at the juncture between arch and lamina.
229
230
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Epiglottis
Ventriculus laryngis
Tuberculum cuneiforme .'
Vallecula epiglottica
Plica pharyngoepiglottica
V Plica ventricularis
Plica vocalis
Plica aryepiglottica
Tuberculum corniculatum
Recessus pyriformis
Incisura interarytaenoidea
Fig. 122. Laryngeal cavity of Ailuropoda from above.
The arytenoid cartilage is massive and irreg-
ular in form, with well-developed processes. The
median processes of the two arytenoids are in con-
tact at the midline. The apex is short and blunt,
the muscular process moderate in length but very
broad and heavy. The corniculate process is a
very short cylindrical projection on the medial
margin of the cartilage. The vocal process is a
keel-like projection on the ventral surface of the
cartilage.
The cuneiform cartilage is a very large L-shaped
structure attached to the apex of the arytenoid.
A small unpaired interarytenoid cartilage lies im-
mediately anterior to the two median processes of
the arytenoid, and marks the posterior limit of the
interarytenoid notch.
C. Muscles of the Larynx
M. aryepiglotticus (fig. 125) arises from the
interarytenoid cartilage, beneath the oblique ary-
tenoid, and extends almost directly ventrad along
the aryepiglottic fold, lying lateral to the ventric-
ular fold, to insert on the base of the epiglottis.
A few of the posterior fibers insert on the antero-
lateral margin of the arytenoid cartilage.
M. cricothyreoideus (fig. 124) is partially di-
visible into straight and oblique portions. The
more superficial pars recta arises from the medial
ventral border of the arch of the cricoid cartilage,
separated by a small interval from its mate of the
opposite side, and passes straight dorsad to its in-
sertion along the dorsal half of the posterior border
of the thyroid cartilage from the level of the infe-
rior tubercle to the inferior cornu. A few of the
superficial fibers are continuous with some of the
posterior fibers of the thyropharyngeal division of
the posterior constrictor of the pharynx. The
deeper pars obliqua arises from the posteroventral
border of the cricoid, and inserts into the posterior
cornu and inner surface of the thyroid cartilage.
A few fibers continue into the cricopharyngeal di-
vision of the posterior pharyngeal constrictor.
M. cricoarytaenoideus posterior (fig. 125) is
a fan-shaped muscle lying on the dorsal surface of
the lamina of the cricoid cartilage. Origin is from
the middle and posterior thirds of the dorsal sur-
face of the cricoid lamina, where it is separated
from its mate by a median keel on the cricoid lam-
ina. The fibers converge anterolaterally, to insert
on the posterior margin of the muscular process of
the arytenoid cartilage.
M. cricoarytaenoideus lateralis arises from
the dorsolateral margin of the cricoid caitilage and
inserts on the anterolateral border of the muscular
DAVIS: THE GIANT PANDA
Proc. medianus
231
Linea obliqua
Cart, interarytenoid
Cornu ant.v.
Cornu post, os hyoid
Cornu post.
Cart, tracheales
Fossa muscularis
Cart, thyreoidea
LATERAL
Cart, cricoidea
Tub. thyreoideum post.
Cart, interarytenoid^ p^ comiculatus
Cart, arytenoid. _/-! l'f<[ ^ p^^ medianus
Proc. muscularis
Incisura thyreoidea post.
Arcus cart, cricoideae
Cart, tracheales
Cornu ant.
Lamina cart, cricoidea
DORSAL
Cart, thyreoidea
Tub. thyreoideum post.
Cornu post.
VENTRAL
Cart, postarytenoid
Cart, cuneiform is
I*roc. medianus
Cart, arytenoid.
FVoc. vocalis
Lig. vocalis
LATERAL
Fig. 123. Laryngeal cartilages of Ailuropoda.
process of the arytenoid cartilage. The anterior
fibers insert into a narrow raphe shared by the
transverse arytenoid.
M. vocalis arises from the thyroid lamina at the
ventral midline, and inserts on the muscular proc-
ess of the arytenoid cartilage. The muscle lies
lateral to the vocal ligament.
M. hyoepiglotticus (fig. 125) is a slender paired
muscle extending from the ceratohyal to the lin-
gual surface of the epiglottis. The fibers overlap
and unite with those of the muscle of the opposite
side at the insertion.
M. thyreoarytaenoideus (fig. 125) arises from
the midventral border of the thyroid cartilage,
passes around the lateral dorsal aspect of the ary-
tenoid cartilage, and inserts on the interarytenoid
cartilage. It is not entirely separable from the
vocal muscle lying deep to it.
232
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Os ceratohyale
Os epihyale
M. ceratohyoideus
Corpus ossis hyoidei
Os thyreohyale
M. hyoglossus (cut)
Insertion m. mylohyoid.
M. constr. phar. med.
M. thyreohyoid.
M. thyreopharyng
M. styloglossus (cut)
constr. phar. med.
Insertion
m. hyoglossus
Origin
m. thyreohyoid.
Membrana
hyothyreoidea
Os stylohyale
Cart, thyreoidea
Insertion m. thyreohyoid.
Origin m. cricothyreoid.
Cart, cricoidea
Insertion m. cricothyreoid.
Origin m. cricopharyngeus
Insertion m. sternothyreoid.
Lig. cricothyreoid. med.
M. cricothyreoideus
M. cricopharyngeus
Trachea
Fig. 124. External laryngeal musculature of Ailuropoda, ventral view. Superficial dissection to left, deeper dissection to right.
M. arytaenoideus obliquus (fig. 125) is a thin
strand of muscle fibers arising from the interary-
tenoid cartilage at the dorsal midline, crossing the
origin of its fellow, and running obliquely anteri-
orly along the aryepiglottic fold to insert on the
epiglottis at the pharyngo-epiglottic fold.
M. arytaenoideus transversus (fig. 125) is a
well-developed paired muscle arising from the mus-
cular process of the arytenoid cartilage and insert-
ing at the midline on the interarytenoid cartilage.
It is overlapped at its insertion by fibers of the
oblique arytenoid, aryepiglottic, and external thy-
roarvtenoid muscles.
D. Discussion of Larynx
Larynxes of Canis latrans, Procyon lotor, Xasna
narica, AiluTus julgens, Ursus tibetanus, U.ameri-
canus (juvenile), and Melursus ursinus were dis-
sected for comparison with Ailuropoda (fig. 126).
Among arctoid carnivores, only the larynx of Cams
familiaris has been well described in the literature.
Albrecht ( 1896) described and compared the mucous
membrane folds of the larynx in several arctoids:
Canis, Vulpes, Otocyon, Procyon, Potos, Ursus, and
several mustelids. Goppert (1894) described the
cartilage of the epiglottis and the cuneiform carti-
lage of Ursus arctos and several mustelids. Owen
Os ceratohyale
DAVIS: THE GIANT PANDA
Corpus ossis hyoidei
M. genioglossus
233
M. ceratohyoideus
Os epihyale
M. hyoepiglotticus
Os thyreohyale
Os stylohyale
Membrana hyothyreoidea
Epiglottis
Os tympanohyale
Cart, thyreoid.'
Proc. muse, cart, aryt
Cart, interarytenoid
Proc. medianus, cart, aryt-
M. arytenoid, obliquus
M. thyreoarytenoid. extemiis
M. arytenoid, transversus
M. cricoarytenoid, posterior
Trachea
Fig. 125. Intrinsic laryngeal musculature of Ailuropoda dorsal view.
(1868) described and figured the laryngeal carti-
lages of Ursus. Fiirbringer (1875) studied the in-
trinsic laryngeal musculature of seventeen species
of Carnivora, including Canis, Procyon, Nasua,
and Ursus.
In general, the larynx is most primitive in the
Ursidae among the arctoids. This is emphasized
by Goppert (1894) for the epiglottal and cuneiform
cartilages, and (1937) for the arytenoids. It is
confirmed in the present study. The larynx is
generally primitive in the Canidae, but with dis-
tinct and characteristic specializations. In the
Procyonidae the larynx is much reduced, in some
respects almost degenerate.
The epiglottis is lanceolate in all arctoids in
which it has been examined. In the Canidae the
angles of the epiglottis are very sharp and the ary-
epiglottic folds are narrow and transverse, giving
a characteristic triangular shape to the anterior
part of the entrance to the larynx. Cuneiform
Cants familiaris
^
Ailurus fulgens
Nasua nariea
MduTSus UTsinug
Ailuropoda melanoUuca
Fig. 126. LarjTigeal cartilages of representative arctoid carnivores, right lateral view. The arj-tenoid and cuneiform
cartilages are shown separately above the main cartilages.
234
DAVIS: THE GIANT PANDA
235
and corniculate tubercles are present, both pairs
lying close to the midline. In the Procyonidae the
epiglottis is reduced, especially its lateral wings.
The aryepiglottic folds are heavy and run obliquely.
A cuneiform tubercle is present, although unsup-
ported by cartilage, but the corniculate tubercle
is completely absent. In the Ursidae and Ailu-
ropoda the aryepiglottic fold is heavy and runs
obliquely, but the line is interrupted at the cunei-
form tubercle. Both cuneiform and corniculate
tubercles are prominent. The ventricular and
vocal folds show little significant variation among
the arctoids examined. They are oriented very
steeply, and the ventriculus is very deep, in the
Canidae.
The thyroid and cricoid cartilages are only
slightly excised at their margins in the Ursidae
and Ailuropoda, and the posterior thyroid notch,
while deep, is very narrow, giving a boxy appear-
ance to the laryngeal skeleton. The hyothyroid,
cricothyroid, and cricotracheal membranes are
correspondingly reduced. The thyroid cornua are
moderately long and subequal. There is a sharply
defined muscular fossa below the posterior cornu.
The posterior thyroid tubercle is large but low.
The cricoid arch is intact but deeply incised at the
ventral midline (Melursus), almost divided ( Ursus
malayanus, Owen), or completely divided {Ailu-
ropoda and our specimen of Ursus americanus) .
In the Canidae the margins of the cartilages are
somewhat more excised than in the Ursidae. The
posterior thyroid notch is very shallow. The an-
terior thyroid cornu is normal, but the posterior
cornu is extremely short, scarcely differentiated
from the thyroid lamina. There is no muscular
fossa, and the posterior thyroid tubercle is small.
The cricoid arch is intact, and its anterior margin
is broadly excised.
In the Procyonidae (including Ailurus) the mar-
gins of the thyroid lamina are deeply excised, in
addition to a very deep posterior thyroid notch.
The laryngeal membranes are very extensive. The
thyroid cornua are approximately normal. Mus-
cular fossa are absent. The posterior thyroid tu-
bercle is enormous and projecting in Nasua and
Ailurus, absent in Procyon. The anterior margin
of the cricoid arch is broadly excised (except Ailu-
rus), and the posterior margin is reflected in lip-
like formation.
The arytenoid is massive and with well-devel-
oped processes in the Ursidae and Ailuropoda.
The median processes of the two arytenoids meet
at the midline. The vocal process is large and
wing-like. The cuneiform cartilage is large and
L-shaped. A rod-like interarytenoid cartilage is
lodged between corniculate and median processes.
In the Canidae the arytenoid resembles that of the
Ursidae but is less massive. The median process
is much reduced. It is notable for the great length
of the corniculate process, which extends back as a
curved finger-like structure beyond the interaryte-
noid incisure. The cuneiform is very large and
irregular in outline, with a long dorsal process.
In the Procyonidae (including Ailurus) the ary-
tenoid is reduced to a triangular flake of cartilage,
the apexes of the triangle representing the apex,
and the muscular and median processes, respec-
tively. The median processes are well separated
at the midline. The corniculate process is entirely
absent {Procyon, Nasua) or represented by a small
elevation {Ailurus). The cuneiform cartilage is en-
tirely absent, but the interarytenoid is present as
a nodule of cartilage.
There do not appear to be any significant differ-
ences in the laryngeal muscles of the Canidae and
Ursidae. These muscles were not dissected in the
Procyonidae.
E. Summary of Larynx
1. The larynx of the Ursidae is the least spe-
cialized among the arctoid carnivores.
2. The larynx of Ailuropoda closely resembles
that of the Ursidae.
3. In the Canidae the larynx shows numerous
characteristic modifications.
4. In the Procyonidae the larynx has under-
gone degenerative modifications. Thyroid and
cricoid are reduced, and the arytenoid and its asso-
ciated cartilages are degenerate.
5. The functional significance of these differ-
ences is unknown.
II. TRACHEA
The trachea (fig. 127) has a length of 270 mm.,
from the base of the cricoid cartilage to the poste-
rior base of the bifurcation of the bronchi. It is
composed of 27 cartilaginous rings, which is the
number estimated by Raven (1936). Several pairs
of rings are partly united, and this gives them a
bifurcated appearance. The diameter of the tra-
chea is 35 mm. (36 mm. in Raven's specimen).
The dorsal membranous part of the rings has a
maximum width of 6 mm.
The bronchi are extremely short, dividing al-
most immediately into eparterial and hyparterial
rami. The base of the bifurcation of the right
bronchus is scarcely farther ectad than the border
of the trachea, but the left bronchus has a length
of 30 mm. before it bifurcates. The right bronchus
has a diameter of 41 mm.; that of the left is only
23 mm.
236
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Trachea
Lobus ant. sin.
Lobus ant. dex
Vv. pulmonales
Lobus med. de.x.
Lobus post. dex.
Ramus A. pulmonalis
Bronchus sin.
Lobus azygos
Lobus post. sin.
Ligg. pulmonales
Fig. 127. Trachea, bronchi, and lungs of Ailuropoda, ventral view.
in. LUNGS
The lungs (fig. 127) are elongate wedge-shaped
structures. They are made up of completely sep-
arate lobes, the lobes of either side being joined
only by the bronchi and a small isthmus of the
serous coat. The left lung consists of two sub-
equal lobes, both larger than any of the lobes of
the right lung. The anterior lobe measures 175
mm. in length, the posterior 165 mm. The ante-
rior and posterior lobes of the right lung are ap-
proximately equal in size, each measuring about
135 mm. in length. The very small right median
lobe is wedged in between the anterior and poste-
rior lobes. The small pointed azygous lobe lies
ventral to the median edge of the right posterior
lobe. It is deeply molded by the posterior vena
cava, which it embraces from the dorsal side. As
in the specimen studied by Raven, the right epar-
terial bronchus supplies only the anterior lobe.
There is a prominent posterior pulmonary liga-
ment at the posterior end of each lung, which
attaches to the diaphragm.
Discussion of Lungs
The form of the lungs is molded by the shape of
the thoracic cavity, the heart, and the diaphragm.
Differences in form attributable to these agents
are evident among carnivores, but scarcely seem
worth discussing here. The most dramatic char-
acter of the lungs among the Carnivora is the dif-
ference in the number of lobes. In the Canidae
(and all Aeluroidea that have been examined) the
left lung is divided into three lobes, whereas in
the Procyonidae (including Ailurus; Carlsson,
1925), Ursidae, and Mustelidae the left lung is di-
vided into only two lobes (Goppert, 1937). Ailu-
ropoda agrees with the second group. The right
lung is divided into four lobes (including the azy-
gous) in all fissiped carnivores.
Secondary reduction of lobation appears to be
correlated primarily with broadening of the thorax
DAVIS: THE GIANT PANDA
237
(Marcus, 1937). No figures are available for the
thoracic index in the Procyonidae, Ursidae, and
Mustelidae, but it is evident from inspection that
the thorax is relatively broader in these than in
the dogs, cats, and civets.
IV. CONCLUSIONS
1 . The respiratory system of Ailuropoda closely
resembles that of the Ursidae.
2. The larynx of the bears and Ailuropoda is
the most primitive among the arctoid Carnivora.
The larynx is specialized, in different directions,
in the Canidae and Procyonidae.
3. Lung lobation is similar in the Procyonidae,
Ursidae, and Mustelidae. The Canidae and all
aeluroid carnivores have one more lobe in the left
lung.
CIRCULATORY SYSTEM
I. HEART
Two hearts were available for study: the sub-
adult heart, fixed in situ, of Su Lin, and the fully
adult heart, preserved in formalin after removal
from the body, of Mei Lan. The description is
based largely on the heart of Su Lin; the adult
heart was not in suitable condition for detailed
study.
The heart, fixed in situ in moderate contraction,
has the form of a slender cone. The longitudinal
diameter gi'eatly exceeds the transverse diameter,
and the apex is pointed. The proportions of the
heart resemble those in the Ursidae, except that
the organ is more slender in Aihiropoda. In the
Canidae the heart is markedly globular.
The heart of Su Lin (empty, without the peri-
cardium, and with the great vessels cut short)
weighs 302 gi-ams, which is 0.5 per cent of total
body weight. This heart measures 92 mm. from
base to apex (apex= coronary sulcus at the origin
of the left longitudinal sulcus),' 79 mm. in trans-
verse diameter (gi-eatest distance between the two
longitudinal sulci), 77 mm. in sagittal diameter
(greatest distance between points intermediate be-
tween the two longitudinal sulci), and 252 mm.
in circumference (maximum circumference around
ventricles). The heart of Mei Lan weighs 530 gi-ams
and measures about 115 mm. from base to apex.
In an old male Tremarctos ornatus, which died
in the Chicago Zoological Park and which weighed
175 pounds at death, the heart formed 0.5 per cent
of body weight. Heart weights given by Crile and
Quiring (1940) represent 0.8 per cent of total body
weight for a fresh specimen of Ursus horribilis
that weighed 310 pounds, 0.6 per cent for a fresh
specimen of Thalarctos maritimus that weighed 440
pounds, and 0.4 per cent for another Thalarctos
that weighed 700 pounds. In the domestic dog
the heart forms about 1.1 per cent of adult body
weight (Ellenberger and Baum, 1943), in the do-
mestic cat about 0.4 per cent (Latimer, 1942).
A. Exterior of the Heart. (Figure 128.)
The left surface (anterior of human anatomy) of
the heart is almost flat, and the right surface is
' For heart measurements I have used the method de-
scribed by Gschwend (1931, Anat. Anz., 72, p. 56).
divided into two planes that meet at an acute an-
gle opposite the left surface. Thus the cross sec-
tion of the heart is triangular. The auricles are
relatively small; the left auricle, much smaller than
the right, measures 35 mm. in diameter, the right
52 mm. The auricles are broadly separated from
one another by the great vessels. The right auri-
cle lies much higher than the left, almost entirely
above the coronary groove. It is wi-apped around
the base of the aorta. The left auricle lies below
the pulmonary artery, mostly below the coronary
gi'oove. Its distal two thirds is appressed against
the left ventricle.
The longitudinal gi'ooves are well marked. The
left is more prominent than the right. The left
longitudinal gi'oove begins near the base of the
pulmonary artery, beneath the left auricle, and
runs diagonally toward the tip of the heart. It
crosses over onto the right surface at the incisura
cordis, well above the apex of the heart. The po-
sition of the incisura cordis is about 20 per cent of
the distance between the apex and base of the heart.
The right longitudinal groove begins at the root of
the posterior vena cava and runs almost straight
toward the tip of the heart. Some distance above
the tip it unites with the left longitudinal groove.
Thus the right ventricle does not reach the tip of
the heart, which is formed entirely by the left ven-
tricle. The conus arteriosus is moderately inflated.
The right atrium is much inflated and almost glob-
ular. The sulcus terminalis appears as a faint
gi'oove beginning between the anterior vena cava
and the wall of the atriiun and running toward the
base of the postcava. The left atrium is much
smaller than the right. Externally the two atria
meet only posteriorly, above the postcava, and
here the boundary between them is very indistinct.
Anteriorly they are broadly separated by the aorta
and pulmonary artery.
B. Interior of the Heart
Atria
Right Atrium. The cavity of the distended
right atrium is much larger than that of the left,
and is much broader than high. The atrium proper
measures about 60 mm. in breadth. Except in the
auricular region the external wall is thin, only
238
DAVIS: THE GIANT PANDA
V. cava ant.
239
Aorta ascendens
Auricula dext.
A. pulmonalis
Conus arteriosus /
Ventriculus dext. ['
FACIES STERNOCOSTALIS
^ V. pulmonalis
Auricula sin.
FACIES DIAPHRAGMATICA
Sulcus longitud. sin.
Incisura cordis
Ventriculus sin.
Fig. 128. Heart of Ailuropoda from the left side.
about a millimeter in thickness. The anterior vena
cava enters the atrium from above, the posterior
vena cava from behind. The crista terminalis,
corresponding in position to the sulcus terminalis,
is a ridge running from the right (anti-septal) side
of the anterior caval orifice toward the postcaval
orifice. It is prominent at first, but quickly fades
out. Pectinate muscles are prominently developed
in the auricle, and are faintly evident on the exter-
nal wall of the atrium nearly to the entrance of the
postcava. The septal wall is smooth.
The tuberculum intervenosum is indistinguish-
able from the crista intervenosa, into which it nor-
mally continues. The tuberculum intervenosum
has the form of a conspicuous ridge on the septal
wall, running apically and to the right between the
orifice of the anterior vena cava and the fossa ovalis.
The fossa ovalis is an inconspicuous shallow and
poorly defined depression, only about 7 mm. in
diameter, bounded anteriorly by the ridge-like tu-
berculum intervenosum. The orifice of the coro-
nary sinus, which is about 7 mm. in diameter, lies
240
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
Cuspis ant.
Conus arteriosus
Valv. semilunares
A. pulmonalis
I
Trabeculae transversae
M. papillaris subart.
Sulcus longitud. sin.
Trabeculae cameae
Incisura cordis
Moderator band"
Fig. 129. Right ventricle of Ailuropoda.
directly below (apicalward of) the entrance of the
postcava.
Left Atrium. The cavity of the atrium proper
is ovate, with the long diameter transverse to the
long axis of the heart. The long diameter meas-
ures about 40 mm. The wall is about 6 mm. thick,
and thus is much heavier than the wall of the right
atrium. The walls of the auricle are almost paper-
thin. The pulmonary veins enter the atrium from
above. The lining of the atrium is completely
smooth and practically devoid of relief. The pe-
ripheral part of the auricle contains a meshwork
of coarse pectinate muscles, some of them free-
standing cylindrical strands. On the internal wall
of the auricle, near its entrance into the atrium,
there is a large pillar-like pectinate muscle, 7 mm.
in diameter, from which smaller strands pass to
the auricular wall. On the septal wall the site of
the foramen ovale is marked by an inconspicuous,
very shallow depression.
Ventricles
Right Ventricle. The right ventricle (fig. 129)
has a triangular cavity, somewhat broader than
high, terminating posteriorly in a long funnel-
DAVIS: THE GIANT PANDA
241
shaped conus arteriosus. The crista supraven-
tricuiaris is short and extends nearly vertically
downward. The ventricular cavity measures about
70 mm. in breadth (measured to base of semilunar
valve, and 58 mm. in height (base to apex). The
conus accounts for about 37 per cent of the total
breadth of the chamber. The external wall has a
maximum thickness (near the base of the conus)
of about 9 mm.; it is thinnest near the apex. The
septal wall is firm, and arches prominently into
the cavity. It is smooth and free of trabeculae
except near the basal groove. The external wall,
on the contrary, is covered with a coarse mesh-
work of ridges, the trabeculae carneae, except in
the conus region. A system of free cord-like tra-
beculae is present on the external wall. There are
four well-developed papillary muscles, situated
near the center of the septal wall. There evidently
was considerable disturbance of the normal devel-
opmental pattern in the right ventricle of Mei Lan,
although the arrangement and proportions of struc-
tures are generally similar to Su Lin and the
Ursidae.
The papillaris subarterialis can scarcely be
said to exist. At its customary site, on the septal
wall near the beginning of the conus, a single
chorda tendinea arises directly from the septum
and passes to the cusp of the septal valve. Imme-
diately behind this chorda, but completely sepa-
rate from it, lies the base of the arteriormost chorda
tendinea propria. In the heart of Mei Lan not
only the papilla, but also the chorda normally aris-
ing therefrom, are completely absent.
Of the four papillary muscles, the first three rep-
resent anterior papillary muscles; the fourth, situ-
ated most posteriorly in the posterior niche of the
ventricle, is the posterior papillary muscle.
The three anterior papillary muscles are sit-
uated in a line, the first two close together, the
posteriormost one somewhat isolated. All arise
from the septum, but the base of each is con-
nected with the external wall by a transverse tra-
becula. The anteriormost papilla, the largest, is
cylindrical, 11 mm. in height by 7.5 mm. in diam-
eter, and terminates in three chordae tendineae
that pass to the anterior cusp. The base of this
papilla is connected to the external wall by two
large plate-like transvei'se trabeculae, the larger of
these 3.5 mm. in diameter. A short but conspic-
uous ridge-like elevation of the septal wall (repre-
senting the moderator band of human anatomy)
passes downward and posteriorly to the base of
the anteriormost papilla. It fuses with the base
of the papilla, where it continues directly into the
uppermost of the two plate-like transverse tra-
beculae. The second papilla stands free of the
septum except at its base. It terminates in a sin-
gle chorda that subdivides and passes to the ante-
rior and posterior cusps. The base of this papilla
is connected to the base of the first papilla and to
the external wall by a stout cylindrical transverse
trabecula, 1.5 mm. in diameter. The third papilla
is slightly smaller than the second, and terminates
in a single chorda that passes to the posterior cusp.
Its ba.se is connected with the external wall by a
short cylindrical transverse trabecula.
A single posterior papillary muscle is situ-
ated in the posterior niche of the ventricle. It is
stout, but shorter than any of the anterior papil-
lae, and has the shape of a flattened cylinder. It
is septal in position, but its base is connected to
the external wall by a short stout transverse tra-
becula. This papilla is two-tipped. A group of
2-3 chordae tendineae arising from each tip rami-
fies to the posterior and septal cusps.
There are no accessory papillary muscles. A
row of 8 direct chordae tendineae arises from
the middle part of the septum, the anteriormost
lying directly behind (septalward of) the subarte-
rial papilla. These are fairly regularly spaced at
intervals of about 7 mm. Each ramifies to the
cusp of the septal valve.
Transverse trabeculae. Ackerknecht (1919)
defines these as more or less cylindrical strands
that (1) are related to the papillae, and (2) cross
the ventricular cavity transversely or obliquely.
Thus he distinguishes the transverse trabeculae,
which contain a part of the conducting system,
from other trabecular structures that often extend
across between septum and external wall. Acker-
knecht interprets these latter structures as modi-
fied trabeculae carneae. In Ailuropoda these two
trabecular systems are topogi'aphically closely re-
lated at the base of the anteriormost papilla. Two
heavy, flattened-cylindrical transverse trabeculae
arise from the base of this papilla and run horizon-
tally to the external wall, where they terminate in
the trabecular meshwork situated there. The up-
permost of these is continuous at its origin with
the moderator band ; these two structures together
form the "trabecula septomarginalis" of Acker-
knecht. Near its origin the upper trabecula gives
off a slender trabecular strand that runs independ-
ently to the meshwork on the external wall. In
addition, the first and second papillae are inter-
connected at their base by a flattened-cylindrical
free trabecula; one slender transverse trabecula
arises from the middle of this and a larger trans-
verse trabecula comes from its attachment to the
second papilla. Both go to the meshwork on the
external wall. Thus four transverse trabeculae,
all inserting into the meshwork, arise from the
anterior papillae.
242
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
From the base of the posterior papilla a short,
stout transverse trabecula passes to the external
wall in the niche region of the ventricle.
Trabeculae carneae. The inner surface of
the whole external wall is covered with very prom-
inent, coarse trabeculae carneae. These are ridges
in high relief, about 3 mm. in diameter, surround-
ing shallow sinuses. Fleshy trabeculae are least
prominent, but still present, on the external wall
in the conus region. The general direction of the
trabecular ridges is horizontal. The septal wall is
smooth and free of trabeculae, except for short,
heavy, pillar-like structures in the basal groove.
Two powerful muscular bands, 14 mm. in diam-
eter, arise from the septum near the base of the
anteriormost papilla and run horizontally to the
external wall, where they insert on the trabecular
ridges. These resemble transverse trabeculae, but
are not connected either with papillae or with the
trabecular meshwork on the external wall, and
therefore are interpreted as trabeculae carneae.
A similar arrangement, except that the trabeculae
were much more slender, was present in one speci-
men of Helarctos.
The trabecular meshwork of cord-like free strands
lies on the external wall at the level of the papillae,
i.e., at about the middle of the external wall. This
system consists of two or three strands, all paral-
leling the transverse axis of the ventricle, with
numerous short thread-like roots arising from the
external wall. There are a few interconnections
between the main strands. The transverse tra-
beculae from the papillae insert into this trabecu-
lar meshwork.
Tricuspid valve. The atrioventricular orifice
is 42 mm. in length. The anterior and septal
(medial) cusps are subequal in size, and the bound-
ary between them is clearly marked. The ante-
rior cusp measures about 40 mm. in breadth. The
posterior cusp, much smaller than the other two,
is clearly bounded from the septal cusp, less dis-
tinctly so from the posterior cusp. No accessory
cusps are evident, but the free margin of each pri-
mary cusp is deeply notched between the attach-
ments of the chordae tendineae, giving it a scalloped
appearance.
The three semilunar valves occupy the usual
position at the base of the pulmonary artery.
Each forms a deep pocket. In the middle of the
free margin of each there is a conspicuous nodulus
of Aranti.
Left Ventricle. The cavity has the form of
an inverted cone, and is smaller than the cavity
of the right ventricle. The external wall has a
maximum thickness of about 16 mm., and thus is
nearly twice as thick as the wall of the right ven-
tricle; it is thinnest at the apex, where it measures
about 9 mm. Except in the conus region, the lin-
ing is thrown up into prominent longitudinal ridges,
much more regular and slightly more prominent
than the trabeculae carneae of the right ventricle.
There is a simple system of free trabecular strands.
Two large and well-formed papillae are present,
nearly equal in size, close together on the exter-
nal wall.
The anterior papillary muscle is pillar-like,
about 11 mm. in diameter, and fused to the ex-
ternal wall except at its tip. The tip is truncated,
and from it arise two very unequal conical struc-
tures from the tips of which the chordae tendineae
are given off. The smaller of these conical struc-
tures, on the medial side of the papilla tip, termi-
nates in five chordae tendineae that ramify to the
external cusp of the bicuspid valve. The larger
conical structure is a long cylinder, 10 mm. long,
terminating in four chordae that ramify to both
valves, but mostly to the septal valve. A single
heavy chorda arises from the base of this cylinder
and ramifies to the septal valve. This gives a total
of ten chordae tendineae. A stout chorda-like
strand arises from the septal side of the tip of the
papilla and runs upward toward the base of the
ventricle, near which it fuses with the septal wall.
At several points along its course this strand is
united to the meshwork of the fleshy trabecular
system.
The posterior papillary muscle is slightly
larger than the anterior papilla, and resembles it
in foi'm except that the tip of the posterior papilla
is more conical. Five chordae tendineae arising
from the tip ramify to the cusps of both valves.
A sixth chorda, arising partly from the papilla
and partly from the external wall, ramifies to both
the septal cusp and the external wall. A large
transverse trabecula arises by several roots from
the septal side of the body of the papilla and runs
up toward the septum, to which it attaches near
the entrance to the conus.
The system of transverse trabeculae consists,
in addition to the strands associated with the pa-
pillae, largely of a single strand running freely and
more or less horizontally over the septal wall near
its middle. Along its course this parent strand is
joined by about six smaller lateral roots arising
from the septal wall, and at each end by a root
from each of the papillary transverse trabeculae.
There is also a loose, coarse meshwork of slightly
smaller strands in the region between the anterior
papilla and the septal wall. Finally, there are a
few very short slender trabeculae in the apical
region.
DAVIS: THE GIANT PANDA
243
Table 2.3. HEART STRUCTURE OF ARCTOID CARNIVORES
Canis* Bassariscus Procyon Ursidae
Form of heart globular subglobular subglobular conical
Right ventricle
Length of conus long very short very short short
Papillaris subart well developed small slightly larger small
Typical no. of anterior
papillae 1 3 3 3
Typical no. of posterior
papillae 3 0? 1 1
Transverse trabeculae moderately stout slender absent slender
Trabecular carneae well developed poorly developed well developed poorly developed
Free trabeculae on external
wall none feeble very feeble yes
Left ventricle
Apical cones on anterior
papillae no no no yes
Trabecular strand on septum . . no yes no yes
Data largely from Ackerknecht (1919).
Ailuropoda
conical
short
absent
3
1
heavy
well developed
yes
yes
yes
The trabeculae carneae form a pattern of
prominent longitudinal ridges covering all the in-
ner surface of the ventricle except the conus. They
tend to converge toward the apex. The ridges
vary in width; the broadest are about 5 mm. wide.
Adjacent ridges are interconnected in many places
by short threadlike strands more or less horizontal
in direction.
The bicuspid valve is much shorter than the
tricuspid, measuring about 20 mm. in length. The
cusps are heavier than those of the tricuspid, and
the two primary cusps are divided by deep inci-
sions into five accessory cusps.
The aortic ostium is situated in the usual place
between the septal valve and the septum, at the
base of a funnel-shaped conus arteriosus. The
semilunar valves guarding the ostium are typical.
There is a nodulus of Aranti in the middle of the
free margin of each valve.
C. Discussion of Heart
The comparative anatomy of the heart in the
Carnivora has been studied by Ackerknecht (1919)
and Simic (1938). Ackerknecht's description of
the papillary muscles and their adnexa was based
on 30 hearts of the domestic dog, one heart of a
European fox, and 15 hearts of the domestic cat.
He was interested primarily in the range of varia-
tion. Simi5 compared the general structure of the
heart in Canis lupus, Vulpes vulpes, Lycaon pictus,
Procyon lotor, Meles meles, Zorilla striata, Felis leo,
Felis tigris, Felis pardus, and Crocuta crocuta. She
listed several characteristic differences between the
Arctoidea and Aeluroidea, but did not attempt to
characterize heart structure at the family level.
It is extraordinary that no one has described the
heart of any species of bear.
I have supplemented the data in the literature
with dissections of the following hearts:
Height in mm. Weight
(base apex) ingms.
Bassariscus astutus (cf ad.) 26 7
Procyon lotor ( cf ad.) 33 19
Procyon lotor (unsexed ad.) 44 42
Helarclos malayanus (d' ad.) 94 345
Helarctos malayanus ( 9 ad.) 98 362
Tremarctos ornatus (cf ad.) 113 397
Ursus americanus (d" juv.) 43 35
Ursus americanus (cf ad.) 127 833
Canis lupus ( cT ad.) 91 265
Felis uncia ( cf) 68 132
Even from this limited material it is evident that
there are characteristic differences among the arc-
toid carnivores. Some of these are listed in the
accompanying table (Table 23). Most relate to
the right ventricle; Ackerknecht found that indi-
vidual variation is also greatest in this ventricle,
which is phylogenetically the most recent part of
the mammalian heart.
At present there is no sure way of deciding what
is primitive and what is specialized in the heart ar-
chitecture of placental mammals, or indeed whether
such terms can be used in comparing heart struc-
ture within the Carnivora.' I shall therefore avoid
such terms here. Whether there is any significant
relationship between structural differences and per-
formance of the heart is likewise unknown.
The heart of the Canidae differs from the heart
of other arctoid carnivores in practically every fea-
ture examined. Some of these differences appear
to be fundamental.
' Ackerknecht "gained the general impression" that the
heart is more primitive in Felis than in Canis, but he does
not give the basis for this opinion.
244
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
There are consistent differences in heart form
among the several families. These reflect the de-
gree of acuteness of the apex, and therefore do not
show up in ratios based on measurements of length
and diameter of the organ. The globular form of
the heart in the Canidae is unlike that of any other
known carnivore. The subglobular form in the
Procyonidae resembles that of the cats. The po-
sition of the incisura cordis seems to be related to
the relative sizes of the two ventricles: where it is
high the relative height of the right ventricle is
less, and vice versa. The incisura is very high in
the Canidae. It is near the apex in the Procyoni-
dae, actually almost at the apex in Bassariscus.
Its position varies among ursid genera; in none is
it as high as in canids or as low as in procyonids.
In Ailuropoda it is as high as in any ursid exam-
ined. It appears to be very high in felids.
The conus arteriosus tends to be short in bears,
although there is considerable variation among
genera. It is longest in Helarctos. The conus is
longer in Canis than in the Ursidae; it is very short
in the Procyonidae.
The papillary muscles of the right ventricle are
situated on the septum in all arctoid carnivores,
whereas in the Aeluroidea the anterior papilla
arises from the external wall. The subarterial
papilla varies in size and position. In the Canidae
and Procyonidae it is well developed (although not
as large as in the cats) and situated directly below
the supraventricular crest. In the Ursidae and
Ailuropoda it is small and situated in the conus
region. Among the arctoids examined there is a
reciprocal relationship between the anterior and
posterior papillae: in the Canidae the anterior pa-
pilla is typically single and shows little variation
in number whereas the posterior is multiple and
extremely variable (modal number 3). In the Pro-
cyonidae and Ursidae, on the contrary, the ante-
rior papilla is multiple and variable (especially in
the Ursidae), and the posterior single and only
slightly variable. Among the five bears exam-
ined, the number of anterior papillae varied be-
tween 2-4 (modal number 3). The number of
direct chordae tendineae is also very high in bears
(8-15). These conditions suggest that the region
of the right ventricle nearest the niche is broad-
ened and least stable in canids, whereas in procyo-
nids and ursids the region toward the conus is
broadened and least stable. The anterior and pos-
terior papillae are situated much higher (near the
center of the septal wall) in the Procyonidae, Ur-
sidae, and Ailuropoda than in the Canidae.
Trabeculae carneae were poorly developed in the
right ventricle of all bear hearts examined, whereas
they were at least moderately prominent in all pro-
cyonids and are described by Ackerknecht as vari-
able but typically well developed in Canis. Typ-
ically absent in the Canidae but very characteristic
of the Procyonidae, Ursidae, and Ailuropoda is a
system of free trabecular strands on the external
wall. These are restricted to a narrow zone more
or less paralleling the transverse axis of the ven-
tricle. Where best developed ( Helarctos) the strands
may form a loose meshwork. The transverse tra-
beculae of the anterior papillary muscle gi-oup in-
sert into this system.
There is much less variation in the left ventricle
than in the right. There were two massive papil-
lae, arising from the external wall, in all speci-
mens examined. The posterior papilla is tj^jically
slightly the larger. In the Ursidae and Ailuropoda
one or more small conical structures, from the tips
of which groups of chordae arise, sit atop the pa-
pillae. These accessory structures are absent in
Canis and the Procyonidae. A transverse trabec-
ula, at its origin looking like a chorda tendinea,
arises from the septal side of the tip of each papilla
and runs up to insert near the base of the ventricle
in all hearts examined. In Bassariscus, the Ursi-
dae, and Ailuropoda a free trabecular strand ex-
tends more or less horizontally over the septal wall.
This strand was usually, but not always, connected
with the transverse trabeculae. It was absent in
the Canidae and in Procyon.
D. Conclusions
1. Most differences in heart structure among
arctoid carnivores involve the right ventricle. The
most characteristic feature of this ventricle is the
increased number of cardinal papillary muscles.
2. The structure of the heart in the Canidae
differs in several respects from that of the Procyon-
idae and Ursidae.
(a) The canid heart has a characteristic form.
(b) In the right ventricle the region nearest the
conus is stable and the niche region is broad-
ened and variable, whereas in the Procyoni-
dae and Ursidae the reverse is true.
(c) In the right ventricle the cardinal papillae
are situated much nearer the basal groove
than in the Procyonidae and Ursidae.
3. The structure of the heart in the Ursidae re-
sembles that of the Procyonidae, but differs in
several respects.
(a) The ui'sid heart has a characteristic form.
(b) In the right ventricle the subarterial papilla
is situated in the conus region.
(c) In the right ventricle there is a well-devel-
oped system of free trabeculae carneae on
the external wall.
DAVIS: THE GIANT PANDA
245
Truncus thyreocervicalis
A. carotis communis dext
A. vertebralis
A. truncus costocervicalis
N. vagus dext.
A. subclavia dext.
A. mammalia int. dext,
Ductus lymphaticus dext.
A. anonyma
Aorta
V. intercostalis ant. dext.
Vena azygos
N. recurrens dext.
N. vagus sin.
A. carotis communis sin.
R. cardiacus ant.
A. mammaria int. sin.
A. subclavia sin.
Ductus thoracicus
R. cardiacus post.
N. recurrens sin.
V. intercostalis
A. intercostalis
A. intercostalis V I
Aorta thoracalis
Fig. 130. Great vessels of the thorax of Ailuropoda.
(d) In the left ventricle the anterior papilla is
furnished! with apical cones.
4. The heart of Ailuropoda resembles that of
the Ursidae in all essential respects.
5. The basis for these differences in heart ar-
chitecture is unknown.
II. ARTERIES
Aorta
The aorta is 45 cm. in length, from the origin of
the subclavian artery to the bifurcation that forms
the common iliacs. Its diameter at the top of the
arch is 26 mm., at the middle of the thorax about
13 mm., and midway between the diaphragm and
the terminal bifurcation (below the origin of the
renal arteries) about 9 mm. The aorta arises from
the left ventricle at the level of the fourth thoracic
vertebra, and extends upward and to the left to
form the aortic arch. The aorta then runs poste-
riorly below the vertebral column, lying just to the
left of the midline until it emerges from between
the crura of the diaphragm, where it moves over
to the midline. The vessel terminates at the level
246
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
of the last lumbar vertebra by breaking up to foi'm
the external iliac, hypogastric, and middle sacral
arteries.
The arch of the aorta gives rise to two branches
in typical carnivore fashion: the innominate and
the much smaller left subclavian. These leave the
top of the arch in close proximity to one another;
they are separated by an interval of less than 5
mm. The smaller visceral branches of the thoracic
aorta were not traced. In the abdomen (fig. 135)
the celiac artery arises at the level of the fourteenth
thoracic vertebra, followed a few millimeters far-
ther posteriorly by the anterior mesenteric. The
renal arteries arise at the level of the first lumbar,
and the posterior mesenteric at the level of the
third lumbar.
Innominate and Common Carotid Arteries
A. anonyma (fig. 130) arises at the level of the
fourth rib, and has a length of 30 mm. before the
left common carotid is given off. The carotids
arise from the innominate independently, the right
coming off 20 mm. farther anterior than the left.
This is contrary to what Raven (1936) found, and
places Ailuropoda in Parson's (1902) class A in-
stead of class B.
Each A. carotis communis (figs. 130, 131)
passes forward alongside the trachea to the level
of the anterior border of the thyroid cartilage.
A. thyreoidea ima arises from the common caro-
tid just anterior to the manubrium sterni and
passes anteriorly on the ventral surface of the
trachea. It supplies the posterior part of the thy-
roid gland and gives off small branches to the tra-
chea. A. thyreoidea anterior (fig. 131) arises at
the level of the third tracheal ring. On the right
side of the neck the anterior thyroid arises as a
large, very short trunk that promptly breaks up
into a number of branches. These supply the an-
terior end of the thyroid gland, the trachea, the
esophagus, and the laryngeal and hyoid muscula-
ture. On the left side the anterior thyroid proper
supplies only the thyroid gland and the intrinsic
laryngeal musculature. A separate branch arising
independently from the carotid 20 mm. farther an-
terior supplies the rest of the laryngeal and hyoid
muscles, the trachea, and the esophagus. At the
anterior border of the larynx the common carotid
divides into the external and internal carotids. As
in other carnivores the internal carotid is smaller
than the external, but in the panda the internal
carotid is relatively large, more than half the diam-
eter of the external carotid, as in bears.
External Carotid Artery
A. carotis externa (fig. 132) curves laterad
around the medial and anterior borders of the di-
gastric muscle. The external maxillary is given
off at the posterior wall of the mandibular fossa,
and beyond this the trunk is continued as the in-
ternal maxillary. The internal maxillary immedi-
ately curves mesad, so that the entire external
carotid trunk describes a pronounced S-curve in
the basicranial region. The external carotid gives
rise to the following branches:
1. A good-sized branch arises from the lateral
wall at the bifurcation into external and internal
carotids. It breaks up at once into twigs for the
large cervical lymph gland and twigs that supply
the anterior end of the sternomastoid muscle and
the posterior end of the digastric.
A. pharyngea ascendens^ (fig. 131) arises as
one of the branches of this trunk. It runs anteri-
orly and mesad to the anterior pharyngeal con-
strictor muscle, then anteriorly along this muscle.
At the posterior border of the levator veli palatini
muscle the trunk bifurcates into palatine and pha-
ryngeal branches of subequal caliber. R. pala-
tinus supplies the anterior pharyngeal and palatine
musculature, ramifies in the glands of the soft pal-
ate, and anastomoses with a descending twig from
the internal maxillary and with the ascending and
descending palatine arteries. A fine muscle twig,
R. m. tensoris tympani, arising from the pala-
tine branch, passes into the middle ear beside the
tendon of the tensor veli palatini, which it sup-
plies, and runs to the tensor tympani muscle, where
it anastomoses with the other tympanic arteries.
R. pharyngeus runs anteriorly beneath the rec-
tus capitis ventralis, continuing in the medial wall
of the eustachian tube to its anterior border, where
it divides into a branch to the pharyngeal tonsil
and another to the dorsal wall of the nasopharynx.
The pharyngeal ramus supplies several minute
Rr. eustachii that ramify in the tubal mucosa.
A. pharyngeotympanica is given off at the level
of the foramen lacerum medium and lies against
the eustachian tube in the musculotubarian canal,
on its way to the middle ear. Near the tympanic
orifice of the eustachian tube the pharyngeotym-
panic sends a fine anastomotic twig that pierces
the wall of the foramen lacerum medium to reach
the internal carotid artery. The pharyngeotym-
panic artery terminates in the tympanic arterial
plexus.
2. A branch arises from the bifurcation of the
carotids and immediately divides into lateral and
medial twigs. The lateral twig accompanies the
external branch of the spinal accessory nerve to
' This vessel is only partly homologous with the ascending
pharyngeal of human anatomy. The posterior meningeal
artery comes from the internal carotid in the panda; the
inferior tympanic arises from the external carotid.
DAVIS: THE GIANT PANDA
247
Nrt. pakUini tnaj
V. palatiiia major
V. palatina minor
V. annularis
V. labialis inf
R. pharyiigeiif!
V. ptcn-R. int
V. facialis externa icut)
V. & X. buccinator.
N. tcmjiprof. ant
N. mnssetericu.'
\. lingtialis
-V. picryg. i,il ^
N, alieolaris inf.
N. nmndibuhri
iV. mylohyoiil
X. chorda tymp
V. for. lac. n
A'', auriculoletiiporalis
H. articiilarif
v. for. postglenoid
V. ma.xilluris inti*rna
V. stylomiLstoidea
R. kI. submaxil!aii.s
-V. facialis
N. glossopfiaryiigeus
N. kypoglossus _
Ganglion cerricalui sup.
X. vagus
V. facialis interna
V. lingualis
N. accessoritts
V. facialis externa (cut)
R. anast. w. v. vertebral,
R. anast. a. pal. major dextra
Foramen incisimm
U. anast. a. sphenopalatina
Sulcus palatitius
A. palatina major
R. anast.
A. palatina minor
. anast. a. pal. asc.
R. m. pteryg. int.
A. temp. prof.
.A. alv. inf,
A. maxillaris interna
R. tons. phar.
A. pharj-ngeotympanica
A. maxillaris ext.
R. m. pieryg. int.
A. temp, superf.
Rr. parotidei
R. auric, prof.
A. trans, faciei
__ R. gl. submaxillaris
Tr. auric, post. & occip.
K. m. pter>-g. int.
A. submentalis
A. lingualis
A. palatina asc.
R. m. trapezius
A. lymph glanduia
carotis externa
A. carotis interna
\. carotis communis
Rr. mm. sternomast. & cleidomast.
V. jugularis externa
v. jugularis interna
A. thyreoidea ant.
Fig. 131. Vessels and nerves of the head of Ailuropoda, inferior view.
the trapezius. The medial branch, A. tympanica
inferior, runs to the lateral border of the foramen
lacerum posterior and accompanies the tympanic
branch of the glossopharyngeal nerve in the mid-
dle ear. The inferior tympanic terminates by
anastomosing with the other tympanic arteries on
the promontorium.
3. A. palatina ascendens (fig. 131) is a slen-
der vessel arising from the medial wall and run-
ning anteriorly and mesad to the pharynx and
posterior part of the palate. It ramifies in the
palatine glands and anastomoses with twigs from
the ascending pharyngeal and posterior palatine
arteries.
4. A, lingualis (fig. 131) is the largest branch
of the external carotid. It arises from the ventral
wall at the level of the hyoid bone, and accom-
panies the hypoglossal nerve anteriorly and me-
sad, deep to the mylohyoid muscle, to the lateral
border of the hyoglossal muscle. Here the artery
248
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
A. temp. prof. ant.
.V. frotitalis
articularis,
Phxus pliriigoiJeus
V. sinus transversus
.V. mamlibularis \\
A. temp, superf.
\'. transv. facei
. temp, superior
.Y. al
A. meningea access}ria
.V. maxillaris \'.
A. temp. prof. post.
A. masseter.
A. temp. prof. post.
R.
Periorbita
\. frontalis
R. anast.V. ophthalm. inf.
-V. supratroch.
.\.dorsaIis nasi
Gi- lat-ritnalis
V. nasofrontalis
Vv. parotidei
V. gl. subma.\illaris
Tr. auric, post. & occip.
A. auric, post. & occip.
V. facialis interna
R. muse.
(eut)
Saccus larrimalis
Lig. orbitalis
Rr. temp. ant.
R. auric, anl.
A. carotis externa ^
A. gl. submaxillaris'
v. maxillaris interna'
A. maxUlaris externa
A. maxillaris interna
\'. sphenopalatina (Vv. pal. desc.)
A. infraorbitalis
Tr. splienopalatina & pal. desc.
* . alv. sup. ant.
facialis prof.
GL orbitoparotidea
,,^- buccinatoria
O/. orbitalis
M. buccinator
alv. sup. post.
A. canal. pter>'g.
A. & v. alveolaris inf.
V. pterj'g. int.
\. anast V. lab. inf.
ab. inf.
V. facialis externa
Fig. 132. Deep vessels and nerves of the head of Ailuropoda, side view.
gives rise to a good-sized R. symphyseus, which
accompanies the hypoglossal nerve along the me-
dial border of the styloglossal muscle, then along
the lateral border of the genioglossus, to the sym-
physeal foramen. Numerous twigs from this branch
supply the sublingual muscles and the floor of the
mouth anterior to the tongue. The main trunk of
the lingual runs beneath the lateral border of the
hyoglossus, into the body of the tongue, where it
ramifies.
Just before passing beneath the mylohyoid, the
lingual gives rise to the small A. submentalis,
which runs forward on the mylohyoideus at its
juncture with the digastric.
5. A slender branch arising from the ventral
wall just anterior to the lingual runs forward to
the pterygoid muscles, which it supplies.
6. A. auricularis posterior + A. occipitalis
(fig. 132) arise by a common trunk at the anterior
border of the mastoid process. The trunk runs
laterad beneath the digastric and parotid gland to
the posterior border of the base of the pinna. Here
the A. sternocleidomastoidea is given off to the
sternomastoid and cleidomastoid muscles.
A. stylomastoidea arises from the posterior
side of the auriculo-occipital trunk at its base. It
runs mesad over the digastric, dividing into a mus-
cular twig to the digastric and the stylomastoid
artery proper. The latter runs beside the facial
nerve to the stylomastoid foramen. A. tympan-
ica posterior is given off in the facial canal, and
accompanies the chorda t\Tnpani nerve into the
middle ear, where it sends a twig to the malleus
and anastomoses with the other tympanic arteries.
A. occipitalis, which is considerably smaller
than the posterior auricular, appears to arise as a
branch of the latter at the boundary between the
sternomastoid and cleidomastoid muscles. The
occipital gves rise to the following branches: Rr.
musculares, arising near the base of the artery,
supply the adjacent muscles and the atlanto-occip-
ital capsule, and send fine nutrient branches into
the back of the skull. R. occipitalis, the termi-
nal part of the artery, runs dorsad beneath the
splenius. At the ventral border of the rectus ca-
pitis posterior major it divides into a superficial
and a deep branch. These ramify to the muscula-
ture in the occipital region and to the nutrient
foramina in the back of the skull, none of the
DAVIS: THE GIANT PANDA
249
twigs extending beyond the lambdoidal crest. The
deep branch also supplies the atlanto-occipital cap-
sule. A slender cutaneous branch runs through to
the skin at the back of the head.
A. auricularis is the continuation of the auric-
ular-occipital trunk after the occipital is given off.
It divides immediately into muscular and auricu-
lar branches. The muscular branch ramifies in the
posterior part of the temporal muscle, also giving
off a twig that supplies the cartilage of the pinna.
A branch, R. mastoideus, arises from the base
of the muscular branch and passes to the mastoid
foramen, which it enters. The auricular branch
then divides into anterior and posterior branches.
A. auricularis posterior is distributed over the
posterior surface of the pinna and to the muscula-
ture of the ear. A. auricularis anterior (fig. 107)
passes around the medial side of the pinna to sup-
ply structures on its anterior side; a large cutane-
ous twig from this branch runs across the top of
the head toward the midline.
7. A. glandularis is a good-sized vessel arising
from the lateral wall of the external carotid oppo-
site and slightly anterior to the preceding trunk.
It passes into the submaxillary gland, where it
ramifies.
8. A. temporalis superficialis (fig. 132) arises,
as a single vessel on the left side of the head and
as two independent but closely associated vessels
on the right, just behind the angular process of the
mandible. Aside from the several small parotid
twigs and the small anterior auricular branch,
which come off near its base, the superficial tem-
poral may be said to divide, after a short trunk,
into two subequal systems : a transverse facial sys-
tem that ramifies below the zygoma, and a tem-
poral system that ramifies above it.
The superficial temporal gives rise to the follow-
ing branches: (a) R. auricularis profundus is the
first branch given off. It is a small twig that runs
to the base of the pinna, (b) Rr. parotidei are
small twigs that arise near the base of the artery
and pass into the parotid gland, (c) A. transversa
facei breaks up into two large branches that ram-
ify over and into the masseter muscle, and a slender
transverse facial branch. The transverse facial
branch is an extremely delicate twig running across
the masseter a short distance below the zygoma;
it accompanies the infraorbital branches of the
facial nerve, and lies above the parotid duct. Twigs
are given off to the masseter, the zygomatic rete,
and cutaneous structures over the masseter; the
vessel terminates by anastomosing with the supe-
rior labial artery, (d) A. zygomaticoorbitalis
(fig. 107) arises from the temporal branch of the
superficial temporal. It runs across the posterior
end of the zygoma and the lower part of the tem-
poral muscle to the orbit, where it anastomoses
with the frontal, supraorbital, and lacrimal arteries.
(e) A. temporalis media is the main continuation
of the temporal trunk after the zygomatico-orbital
branch is given off. It runs up vertically across
the posterior part of the zygoma, dividing into
anterior and posterior branches as it passes over
the upper edge of the zygoma. Both of these
branches ramify through the substance of the tem-
poral muscle, (f) R. temporalis superficialis
(fig. 107) is a slender twig arising from the zygo-
matico-orbital artery midway between the eye and
the ear. It passes up onto the top of the head just
superficial to the temporal aponeurosis, where it
ramifies into an extremely delicate rete in the pari-
etal and posterior frontal regions.
At the angular process of the mandible the ex-
ternal carotid gives off the very small external
maxillary, beyond which the trunk continues on
the medial side of the mandible as the internal
maxillary.
A. maxillaris externa (fig. 107), which has none
of the cervical branches that arise from it in man,
is a slender vessel running across the ventral part
of the masseter. Beyond the edge of the digastric
it is accompanied by the anterior facial vein. Nu-
merous fine twigs are given off to the masseter, and
at the posterior end of the exposed part of the in-
ferior alveobuccal (molar) gland the vessel divides
into the superior and inferior labial arteries. A.
labialis inferior (fig. 107) runs anteriorly along
the inferior border of the molar gland, to which it
gives off twigs, anastomosing anteriorly with the
mental branch of the inferior alveolar artery. A.
labialis superior (fig. 107) is larger than the in-
ferior labial. It passes anteriorly along the supe-
rior border of the molar gland, into which it sends
twigs, and along the base of the upper lip. Ante-
riorly it anastomoses with branches of the infra-
orbital artery. A. angularis is a slender branch
arising from the superior labial directly below the
eye, and passing up across the anterior root of the
zygoma into the orbit.
The Internal Maxillary Artery
A. maxillaris interna (figs. 131, 132) is so much
larger than the external maxillary artery that it
appears to be the continuation of the external caro-
tid trunk, with the external maxillary only one of
the lesser lateral branches. It arises at the poste-
rior border of the mandible, just above the angular
process, and arches forward and upward around
the condyle, lying between the external and inter-
nal pterygoid muscles. The vessel continues into
the space between the coronoid process and the
250
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
skull, terminating near the sphenopalatine fora-
men by dividing into the infraorbital artery and a
trunk for the sphenopalatine and descending pala-
tine arteries. There is no alisphenoid canal.
The internal maxillary gives rise to the following
branches (fig. 132):
L A. alveolaris inferior arises at the inferior
border of the temporal muscle and passes forward
and slightly downward to the mandibular foramen.
The artery lies below the inferior alveolar nerve
as they enter the foramen. The mental branches
emerge from the mandible through the mental fora-
mina, accompanying the corresponding branches
of the nerve.
2. A. temporalis profunda posterior comes
off at the neck of the mandible, passing to the tem-
poral fossa between the internal and external ptery-
goid muscles. Here it divides into posterior and
anterior branches.
The posterior branch gives off a slender R. ar-
ticularis near its base, which passes to the mandib-
ular articulation. Posterior deep temporal vessels
pass back over the root of the zygoma, one of them
entering a nutrient foramen in the temporal bone
at the root of the zygoma, while another anasto-
moses with a twig of the occipital artery near the
lambdoidal crest. A. masseterica, arising as one
of the branches of the posterior branch, arches
around behind the coronoid process, to enter the
masseter muscle, where it ramifies.
The anterior branch of the posterior deep tem-
poral ramifies in the anterior part of the temporal
fossa, beneath the temporal muscle.
3. A. tympanica anterior is a slender vessel
arising at the same level as the deep temporal. It
passes caudad across the external pterygoid mus-
cle, joining the chorda tympani nerve and passing
with it into the petrotympanic fissure. A twig,
given off from the anterior tympanic before it
reaches the fissure, anastomoses with the ascend-
ing pharyngeal artery.
4. A. meningea media is a small twig, con-
siderably smaller than the accessory meningeal,
arising from the internal maxillary just beyond
the temporalis profunda posterior. In the panda
it is not the main source of the meningeal circula-
tion. It joins the trunk of the mandibular nerve
and passes beside it into the foramen ovale. With-
in the cranial cavity the vessel anastomoses with
the accessory meningeal.
5. Rr. pterygoidei, arising from the internal
maxillary along its course, supply the external and
internal pterygoid muscles. A twig associated
with these goes to the orbital gland.
6. A. meningea accessoria is a slender vessel
that enters the orbital fissure, where it lies beside
the maxillary nerve. Within the cranial cavity it
receives the middle meningeal artery, then runs
posteriorly beside the semilunar ganglion to the
tip of the temporal lobe of the brain, where it
breaks up into three branches. These form the
main blood supply to the dura ( fig. 143) ; this was
verified on two specimens. The first branch is dis-
tributed over the frontal lobe; the second passes
up in the lateral cerebral fissure, and is distributed
to the adjacent parts of the frontal and temporal
lobes and to the parietal lobe; the third supplies
the dura over the ventral and posterior parts of the
temporal lobe.
7. .\. orbitalis fophthalmica of authors) is a
good-sized vessel, only a little smaller than the
deep temporal, arising from the internal maxillary
at the anterior end of the internal pterygoid mus-
cle, about 10 mm. beyond the origin of the poste-
rior deep temporal artery. It passes forward and
upward, lying external to the maxillary nerve, to
pierce the ventral wall of the periorbita at about
its posterior third.
Before entering the orbit, the orbital artery gives
rise to an anterior deep temporal branch, which
passes across the periorbita to the anterior part of
the temporal fossa, where it ramifies. The termi-
nal twigs of this vessel pass out of the temporal
fossa onto the frontal area of the head.
As it pierces the periorbita, the orbital artery
gives rise to a posterior and an anterior branch of
approximately equal size, which arise from oppo-
site sides of the parent tiunk. The posterior branch
turns posteriorly, passing beneath the ophthalmic
nerve and through the wall of the superior oph-
thalmic vein. It passes inside the vein through
the orbital fissui-e into the cranial cavity. The
anterior branch, A. lacrimalis, accompanies the
lacrimal nerve forward along the lateral rectus
muscle of the eye. At about the middle of the mus-
cle the artery bifurcates into a muscular and a lac-
rimal ramus. The muscular ramus supplies the
lateral and inferior recti and the inferior oblique,
and supplies an anastomotic twig to one of the
ciliary arteries, while the lacrimal ramus continues
forward to the lacrimal gland.
Immediately after entering the orbit the orbital
artery divides into two equal-sized trunks. The
more supei-ficial trunk, which lies external to the
ocular muscles, supplies structures outside the or-
bit, terminating as the ethmoidal artery. The
deeper trunk arches around the optic nerve, sup-
pljing all the structures within the orbit and anas-
tomosing with the ophthalmic artery.
DAVIS: THE GIANT PANDA
251
A. zygoma tica arises from the superficial trunk
of the orbital artery as the latter crosses beneath
the ophthalmic nerve. Accompanying the paired
zygomatic nerve along the lateral border of M. rec-
tus superior, it pierces the orbital ligament and
emerges near the posterior corner of the eye. The
terminal twigs of the vessel ramify in the super-
ficial area immediately behind the eye.
After giving off the zygomatic branch, the super-
ficial trunk passes across the proximal parts of the
ocular muscles to the ethmoidal foramen. Just
before entering the foramen it gives rise to A.
frontalis, which pierces the dorsal wall of the
periorbita along with the frontal nerve and the
superior ophthalmic vein (fig. 107) ; all three struc-
tures emerge above the eye, where the artery gives
off a small anterior A. dorsalis nasi, then arches
posteriorly to anastomose with a twig of the zygo-
matico-orbital artery. Beyond the origin of the
frontal artery the main trunk is continued into the
ethmoidal foramen as R. ethmoidalis, which
unites with the ethmoidal artery below the olfac-
tory bulbs (p. 253).
The deeper trunk of the orbital artery passes
between M. rectus superior and M. retractor oculi,
arches around to the deep side of the optic nerve,
and anastomoses with the ophthalmic artery to
form the minute central retinal artery. A. cen-
tralis retinae enters the optic nerve 4 mm. behind
the eyeball, and passes to the eye within the nerve.
Numerous muscular twigs arising from the deeper
trunk of the orbital artery supply M. rectus supe-
rior, M. levator palpebrae superior, M. retractor
oculi, M. rectus medialis, and M. rectus inferior.
Two of these twigs terminate by anastomosing
with the muscular ramus of the lacrimal artery.
Aa. ciliares arise from one or more of the muscu-
lar twigs and pass forward alongside the optic nerve
to the eye.
8. A. temporalis profunda anterior (fig. 132)
arises from the internal maxillary directly opposite
the origin of the orbital artery. It ramifies in the
most anterior part of the temporal muscle, one or
more of its delicate terminal branches emerging on
the face below the eye and ramifying over the an-
terior part of the zygoma. A. buccinatoria arises
from the trunk of the anterior deep temporal. It
joins the buccinator nerve and passes with it to the
buccinator muscle.
Beyond the point where the orbital and ante-
rior deep temporal arteries arise, the internal max-
illary corresponds to the "third part of the internal
maxillary" of human anatomy. The vessel passes
upward and forward toward the sphenopalatine
foramen, giving rise to the following branches:
9. A. palatina minor (fig. 131) arises at the
posterior border of the alveolar prominence of
the last molar tooth. It immediately arches me-
sad and ventrad, accompanying the posterior pala-
tine nerve along the anterior border of the internal
pterygoid muscle down to the prominent notch in
the outer border of the vertical pterygoid plate
immediately behind the last molar. After leaving
the notch the vessel bifurcates ; an anterior branch
runs forward along the medial border of the last
molar tooth, to anastomose with the major pala-
tine artery; and a posterior branch runs caudad
along the soft palate to anastomose with the major
palatine. Twigs from the posterior branch ramify
to the palatine glands and other structures in the
roof of the pharynx, and a twig from the anastomo-
sis with the major palatine goes to the auditory
tube.
10. A. infraorbitalis (fig. 132), the more lat-
eral of the two terminal branches of the internal
maxillary, accompanies the infraorbital nerve to
the infraorbital foramen. On emerging from the
foramen it ramifies over the lateral side of the nose
(fig. 107). Alveolar branches (Aa. alveolares su-
periores) from this part of the vessel supply the
premolars, canine, and incisors. A. alveolaris
superior posterior arises from the base of the
infraorbital and pursues a tortuous course back
over the alveolar prominence of the last molar,
giving off niunerous twigs that enter the minute
foramina in this region. A. alveolaris superior
media arises a few millimeters farther forward.
It runs forward, ramifying twigs to the area over
the anterior part of the last molar and the next
tooth forward (M'). A. malaris (Bradley) arises
from the infraorbital just before the latter enters
the foramen. It runs out at the anteroventral
corner of the orbit, lying between the periorbita
and the preorbital fat. Branches supply the lower
eyelid and the lacrimal sac, after which the trunk
continues onto the face in front of the eye.
The medial terminal branch of the internal max-
illary is a short trunk that divides just before
reaching the closely juxtaposed sphenopalatine fo-
ramen and pterygopalatine canal to form the sphe-
nopalatine and descending palatine arteries. A.
sphenopalatina passes into the nose through the
sphenopalatine foramen A. palatina descend-
ens reaches the posterior part of the hard palate
through the pterygopalatine canal. Upon emerg-
ing onto the palate through the posterior palatine
foramen, the vessel divides into anterior palatine
and posterior anastomotic branches. A. palatina
anterior (palatina major) considerably exceeds the
posterior anastomotic in caliber. It runs forward
252
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
in the mucoperiosteum of the hard palate to the in-
cisive foramen, where it anastomoses with the
sphenopalatine artery. The groove for this artery
can be seen on the skull, running forward not far
from the alveolar border. The posterior, anasto-
motic branch passes backward along the border of
the last molar tooth, to anastomose with the minor
palatine artery at the notch in the outer border of
the pterygoid plate.
Internal Carotid Artery
The internal carotid runs forward and mesad
from the bifurcation of the common carotid, arch-
ing dorsad around the medial border of the origin
of the digastric muscle, to enter the foramen lac-
erum posterior. At the level of the paroccipital
process it gives off the posterior meningeal artery.
A. tneningea posterior sends a minute R. sinus
transversus into the foramen lacerum posterior,
supplies a twig to the adjacent cranial nerves, and
then enters the hypoglossal canal. Within the skull
the posterior meningeal ramifies to the dura of the
posterior cranial fossa, and anastomoses with the
basilar artery.
As it enters the foramen lacerum posterior, the
internal carotid is situated anterior to the cranial
nerves passing out of the foramen, and laterad of
the internal carotid (sympathetic) nerves. Just
inside the foramen the artery enters the carotid
canal, within which it passes through the middle
ear. In the middle ear the carotid canal runs for-
ward and slightly mesad, and is situated below
and at first in contact with the petrosal, lying ven-
trad and slightly mesad of the cochlea (fig. 159).
A fine anastomotic twig from the ascending pha-
ryngeal artery joins the internal carotid at the
juncture of the foramen lacerum medium with the
anteromedial part of the carotid canal. The in-
ternal carotid gives off nutrient twigs to the walls
of its canal. Emerging from the carotid canal, the
artery enters the cavernous sinus. Immediately
after entering the sinus it forms a tight knot by
arching first posteriorly, then anteriorly upon it-
self. This is followed in the vicinity of the sella
turcica by a tight S-loop, all of which gi-eatly in-
creases the length of the vessel ; while the distance
traversed within the sinus (from the carotid fora-
men to the anterior border of the sella) is only
22 mm., the length of the vessel is 68 mm.' The
internal carotid emerges from the sinus in the vi-
cinity of the tuberculum sellae, and terminates
several millimeters anterior to the optic chiasma
by dividing into the anterior and middle cerebral
arteries.
' Tandler (1899) gives the corresponding length of this
vessel in a polar bear as 160 mm. (see also p. 257).
The internal carotid gives rise to the following
branches :
1. A. communicans posterior arises from
the internal carotid as soon as it emerges from the
sinus. It is a good-sized vessel, exceeding the pos-
terior cerebral in caliber, that nms backward across
the base of the brain to join the posterior cerebral.
Near its origin, the posterior communicating ar-
tery gives rise to the A. chorioidea, which is
joined by a twig from the internal carotid before
ramifying to the choroid plexus. Farther poste-
riorly it gives off a good-sized hippocampal twig to
the hippocampal gyrus.
2. R. chorioidea, which joins the choroid ar-
tery as described above, arises about midway be-
tween the origin of the communicans posterior and
the terminal bifurcation of the internal carotid.
3. A. ophthalmica is present on the right side
only ; the origin of the corresponding blood supply
on the left side was not traced. The vessel arises
from the internal carotid just before its terminal
bifurcation, and enters the orbit through the optic
foramen. During its course it makes a spiral revo-
lution of 180 around the optic nerve. Situated at
first laterad of the nerve, it enters the optic fora-
men lying dorsad of it, finally emerging from the
foramen into the orbit on the medial side of the
nerve. In the orbit the vessel terminates by anas-
tomosing with the deep trunk of the orbital artery
to form the central retinal artery. -
4. A. cerebri media, the larger of the two
terminal branches of the internal carotid, arches
laterad around the temporal pole into the lateral
fissure where it ramifies to the outer surfaces of
the frontal, parietal, and occipital lobes. Near its
origin the middle cerebral divides into a pair of
parallel vessels (these arise separately on the left
side), which reunite into a common trunk as they
enter the lateral fissure.
5. A. cerebri anterior, the smaller of the ter-
minal vessels, runs toward the midline above the
optic nerve. At the midline it unites with its mate
from the opposite side to form a common trunk
(there is consequently no A. communicans an-
terior), which immediately arches dorsad into the
longitudinal fissure. At the juncture of the two
anterior cerebral arteries the large median eth-
moidal artery, which equals the common anterior
cerebral trunk in caliber, is also given off.
6. A. ethmoidalis interna appears to be some-
what anomalous. The ethmoidal circulation arises
from the anterior cerebrals in the form of three
vessels: a very large median artery flanked on
- Most of the ophthalmic circulation of man has been
taken over by the orbital artery in the panda and related
animals.
I
DAVIS: THE GIANT PANDA
253
either side by a much smaller artery. The median
artery is tied in with the orbital circulation via the
ethmoidal foramen, while the lateral arteries run
directly to the cribriform plate.
J The median ethmoidal artery runs foi-wai-d in
the dura immediately below the longitudinal fis-
sure. Just proximad of the olfactory bulbs it is
joined by a large branch that represents the com-
bined ethmoidal rami of the two orbital circulations.
The vessel then continues forward, breaking up
below and between the olfactory bulbs into numer-
ous terminal branches that pass into the cribriform
plate. A. meningea anterior arises as a fine
twig from the orbital division of the ethmoidal, and
ramifies to the dura of the anterior fossa.
The lateral ethmoidal arteries arch toward the
midline at the posterior border of the olfactory
bulbs, continuing between the bulbs into the crib-
riform plate.
The Subclavian Artery
The left subclavian arises from the convex side
of the arch of the aorta, immediately beyond the
origin of the innominate; the bases of these two
arteries are almost in contact. The right subcla-
vian begins much farther craniad, as the continua-
tion of the innominate after the right common
carotid is given off. Both subclavians have the
same relations beyond the origin of the right sub-
clavian (about from the posterior border of the
first rib). Beyond the origin of the thyi-ocervical
axis the subclavian is continued as the axillary
artery. The subclavian gives off the following
branches: (1) the vertebral; (2) the internal mam-
mary; (3) the thyrocervical trunk; and (4) the
costocervical trunk.
1. A. vertebralis (fig. 130) arises from the dor-
sal side of the subclavian just anterior to the costo-
cervical trunk, to which it corresponds in size. It
passes forward and upward around the M. longus
colli, to enter the transverse foramen of the sixth
cervical vertebra. Passing craniad thi'ough the
transverse foramina of succeeding cervical verte-
brae from the sixth to the first, it reaches the alar
foramen in the atlas greatly reduced in caliber be-
cause of the large muscle branches to which it has
given rise. Turning mesad through the atlantal
foramen, the vessel reaches the spinal canal of the
atlas, where it turns forward again and passes into
the skull through the foramen magnum, lying im-
mediately above the atlanto-occipital articulation.
Within the skull the artery lies at first beside the
medulla, then, between the origins of the first spi-
nal and twelfth cranial nerves, it turns toward the
midline, terminating on the pyramid about 15 mm.
caudad of the pons by uniting with the vertebral
artery of the opposite side to form the unpaired
A. basilaris. On the left side the basilar also re-
ceives an anastomotic twig from the internal caro-
tid; this twig arose outside the skull, entering the
cranial cavity through the condylar foramen. The
basilar artery runs forward in the ventral median
fissure and across the ventral surface of the pons
to the anterior border of the pons, where it termi-
nates by dividing into the two superior cerebellar
arteries (not into the posterior cerebrals, as it does
in man). For a short distance beyond its origin
the basilar is composed of two trunks lying side by
side, but these soon fuse; this condition is probably
an individual anomaly.
The vertebral artery gives rise to the following
branches:
(a) Rr. musculares arise at the intervertebral
spaces, one to each space. These are very large
vessels that pass upward between adjacent trans-
verse processes to ramify in the dorsal axial mus-
culatui'e. Near its base each vessel gives off a slen-
der twig (R. spinalis) that passes through the in-
tervertebral foramen into the spinal canal.
(b) A. spinalis posterior' is a threadlike vessel
that winds caudad along the side of the medulla
to the dorsum of the cord. The paired vessel may
be seen lying in the dorsal lateral sulci of the cord
in a section through the neck made at the fourth
cervical vertebra.
(c) A. spinalis anterior is unpaired in the ani-
mal dissected, and considerably exceeds the pos-
terior spinal in caliber. It arises from the left
vertebral artery at the midline, and runs caudad
on the ventral surface of the medulla and cord.
The branches from the basilar artery are:
(d) A. cerebelli inferior posterior arises from
the basilar (vertebral?) at about the middle of the
olive, and (e) A. cerebelli inferior anterior at
about the posterior third of the pons. These two
vessels form a very loose rete on the inferior sur-
face of the cerebellum, to which they send numer-
ous twigs, eventually uniting at the postero-infer-
ior part of the cerebellum to form a common tmnk
that plunges into the substance of the cerebellum.
(f) A. auditiva interna arises as a delicate
twig from the anterior inferior cerebellar artery.
It accompanies the auditory and facial nerves into
the internal acousticomeatus.
(g) Rr. ad ponteni are given off from the basi-
lar as it cros.ses the pons.
(h) A. cerebelli superior, paired to form the
terminal branches of the basilar artery, arises at
the anterior border of the pons and runs laterad
' No structure corresponding to the R. meningeus of
human anatomy could be found.
254
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
to the anterior surface of the cerebellum. It is
separated from the posterior cerebral artery by the
oculomotor nerve, as in man.
Near its origin the superior cerebellar artery re-
ceives the posterior communicating branch, which
runs caudad from the internal carotid. At this
juncture a good-sized middle thalamic twig is given
off, on the left side only, to the thalamus; no cor-
responding structure is present on the right side.
(\) A. cerebri posterior arises from the poste-
rior communicating branch (at about its posterior
third), and hence actually belongs to the internal
carotid circulation rather than to the vertebral.
It is a slender vessel, considerably smaller than the
superior cerebellar, that runs laterad, caudad, and
dorsad into the notch between the cerebrum and
the cerebellum, eventually supplying the posterior
part of the cerebrum.
2. A. mammaria interna (fig. 130) takes ori-
gin from the ventral wall of the subclavian, imme-
diately opposite the origin of the vertebral artery
and costocervical trunk. Extending obliquely ven-
trad, caudad, and mesad, it meets the internal
mammary vein which descends on the opposite
side of the vena cava, in the space between the
second and third costal cartilages. The artery and
vein pass beneath the transverse thoracic muscle
side by side, about 10 mm. laterad of the sternum.
They pass straight caudad as far as the fifth costal
cartilage, then gi-adually curve toward the midline.
The artery is almost in contact with the tip of the
xiphoid cartilage.
In each intercostal space the internal mammary
artery gives off the usual R. perforans medially
and a R. intercostalis laterally. A. thymica
arises in the first intercostal space and runs trans-
versely to the thjTTius. Beyond the last rib carti-
lage the internal mammary is continued as the
anterior epigastric artery.
3. Truncus thyreocervicalis (fig. 130) arises
from the medial wall of the subclavian about 15
mm. beyond the origin of the internal mammary
artery. It runs forward and outward, ventrad of
the brachial plexus and closely applied to the ex-
ternal jugular vein. The thyrocervical trunk gives
off three branches. The first and smallest (cervi-
calis ascendens of Reighard and Jennings) gives off
a twig that supplies the sternomastoideus, sterno-
hyoideus, and adjacent muscles; the rest of this
branch supplies the posterior cervical lymph gland
and a part of the clavotrapezius. The second
branch supplies the proximal part of the clavo-
trapezius and adjacent muscles.
The third branch, A. transversa colli, is the
largest and appears to be the direct continuation
of the thyrocervical trunk. It passes up around
the shoulder to emerge at the scapulohumeral ar-
ticulation, where it lies between the acromiotra-
pezius and the supraspinatus. The transverse
cervical divides just above the scapulohumeral ar-
ticulation to form anterior and posterior rami. A
third branch, only slightly smaller in size, runs
forward into the clavotrapezius.
R. niedialis (descendens, BNA) runs dorso-
caudad between the rhomboideus and the sub-
scapularis, then turns caudad just before the
coracovertebral border of the scapula is reached,
passing deep to the rhomboids and levator scap-
ulae. Opposite the infraspinous fossa a branch is
sent outward and over the vertebral border of the
scapula into the infraspinous fossa, where it anas-
tomoses with the termini of the circumflex scap-
ular and the thoracodorsalis. Other branches
supply the rhomboids, the latissimus, the spino-
trapezius, the serratus, and the subscapularis. The
branch to the latissimus descends along the ante-
rior border of this muscle, sending off short lateral
twigs into the muscle, and eventually anastomos-
ing with an ascending branch of the thoraco-
dorsalis. The main trunk of the medial ramus
continues beyond the border of the scapula, to
anastomose with the sixth intercostal artery.
R. lateralis (ascendens, BNA) passes across the
supraspinatus caudad of the occipitoscapularis.
Numerous twigs are sent to the occipitoscapularis
and spinotrapezius, other twigs entering the supra-
spinatus fossa to participate in the supraspinatus
anastomosis. Near the coracovertebral angle of
the scapula it sends a terminal twig down into the
supraspinous fossa, which anastomoses with the
terminus of the transverse scapular.
Twigs from the lateral ramus pass across M.
supraspinatus to the proximal part of M. acromio-
trapezius. The most dorsal of these sends a twig
down along the scapular spine, which receives twigs
from the circumflex scapular, transverse scapular,
and external circumflex humeral arteries before it
reaches the acromial process of the scapula. This
branch is the main source of the Rete acromiale.
Other branches from the external circumflex hu-
meral and transverse scapular arteries pass across
the neck of the scapula, and form the other roots
of the rete.
Since the posterior thyroid artery is absent, the
thyrocervical trunk has no relation with the thy-
roid gland.
4. Truncus costocervicalis dextra (fig. 130)
is the first branch given off from the right subcla-
vian. It arises from the dorsal side of the artery,
immediately caudad of the origin of the vertebral
artery, i.e. at the anterior border of the first rib.
Arching upward just outside the pleura, it bifur-
DAVIS: THE GIANT PANDA
255
cates near the articulation of the fiist rib. One
branch, A. intercostalis suprema, passes back-
ward just inside the ribs, giving oflF the usual
branches to the intercostal spaces. The other
branch, A. cervicalis profunda, immediately
passes dorsad between the eighth cervical and first
thoracic nerves, then between the necks of the
first and second ribs. The vessel emerges on the
back of the neck between the longissimus dorsi and
multifidus cervicus muscles, where it divides into
anterior and posterior branches. The anterior
branch ramifies in the biventer cervicis; the pos-
terior branch supplies the longissimus dorsi and
multifidus cervicis.
The left costocervical trunk arises from the left
vertebral artery. It passes dorsad between the
seventh and eighth cervical nerves, giving off a
small intercostalis suprema to the first intercostal
space. The remainder of the vessel continues dor-
sad as the cervicalis profunda, passing between
the seventh cervical vertebra and the neck of the
first rib, beyond which it parallels the course of its
fellow on the opposite side.
Axillary Artery
A. axillaris (figs. 133, 134) is the distal continu-
ation of the subclavian beyond the origin of the
thyrocervical axis. The proximal part of the ar-
tery lies between the brachial plexus (dorsad),
where it is situated between the seventh cervical
and first thoracic nerves and immediately ventrad
of the eighth cervical nerve, and the axillary vein
(ventrad). With the foreleg in an extended posi-
tion the artery curves outward and slightly back-
ward into the leg, where it becomes the brachial
artery beyond the origin of the subscapular trunk.
The axillary artery gives rise to the following
branches: (1) the transverse scapular; (2) the an-
terior thoracic; (3) the thoracoacromial; (4) the
lateral thoracic; (5) the subscapular; (6) the in-
ternal humeral circumflex; and (7) the external
humeral circumflex.
1. A. transversa scapulae (fig. 133) is the first
branch given off by the axillary. It is a good-sized
branch arising from the convex side of the curve of
the axillary as the latter arches back from the first
rib. Running forward, outward and upward, par-
allel with the transverse cervical artery, it gives
off a twig to the anterior division of the superficial
pectoral as it passes around the shoulder joint to
enter the space between M. suprascapularis and
M. infraspinatus. At this point the vessel breaks
up into a number of smaller branches. Of these,
superficial rami supply the adjacent parts of the
supraspinatus and subscapularis, while the largest
branch, which appears to be the direct continua-
tion of the transverse scapular, passes through the
scapular notch onto the supraspinous fossa of the
scapula. Here the larger of two branches ramifies
in the supraspinous fossa, eventually anastomosing
with the posterior branch of the transverse cervical
artery near the vertebral border of the scapula;
twigs from this branch pass toward the scapular
spine, where they participate in the acromial rete.
A smaller branch passes across the neck of the
scapula, at the base of the scapular spine, into the
infraspinous fossa, where it ramifies and anasto-
moses with branches of the circumflex humeral
scapular artery near the glenoid border and with
the descending branch of the transverse cervical
artery near the vertebral border. This branch also
contributes a twig to the acromial rete.
2. A. thoracalis anterior (fig. 133) is a small
vessel arising from the posterior wall of the axillary
artery immediately beyond the border of the first
rib. It runs caudad across the ventral part of the
first intercostal space, which it supplies. It is ac-
companied by a corresponding vein.
3. A. thoracoacromialis arises from the ante-
rior wall of the axillary immediately beside and
internal to the origin of the transverse scapular,
which it slightly exceeds in caliber. Passing dis-
tad between the anterior and posterior divisions of
the pectoral muscle, the thoracoacromialis gives
off numerous twigs to both layers of the pectoral
musculature, the humeral end of the clavotrape-
zius and the acromiodelteus.
The main trunk, greatly reduced in caliber,
pierces the tendon of the pectoral profundus below
the head of the humerus and divides to form as-
cending and descending rami that run along the
pectoral ridge of the humerus. The ascending ra-
mus passes up along the pectoral ridge, pierces the
anterior superficial pectoral muscle near the greater
tuberosity, and so emerges onto the bicipital groove.
The main part of the branch enters a nutrient fora-
men in the bicipital groove, while a smaller twig
continues beneath the tendon of the biceps, where
it anastomoses with a branch of the internal hu-
meral circumflex. The descending ramus runs dis-
tad along the ridge, to anastomose with a twig
from the profunda brachii at the distal border of
the tendon of the teres major.
4. A. thoracalis lateralis (fig. 133) arises from
the posterior wall of the axillary, 17 mm. distad of
the origin of the thoracoacromial artery. It passes
caudad, giving off branches to the pectoralis pro-
fundus, the panniculus, and the serratus. Inter-
costal branches to the second to fourth intercostal
spaces anastomose with the aortic intercostals.
Twigs are also sent to the axillary lymph glands.
I
a
o
a
a
3
o
s
c
256
DAVIS: THE GIANT PANDA
257
5. A. subscapularis (fig. 133) takes origin from
a trunk that gives rise also to the two circumflex
humeral arteries and a large vessel that furnishes
the main blood supply to the latissimus, subscap-
ular, and adjacent muscles. This trunk arises from
the anterior wall of the axillary about 35 mm. dis-
tad of the origin of the thoracoacromial (i.e., oppo-
site the ventral border of the teres minor), and
beneath the pectoral musculature. The trunk
passes laterally (externally) through the interval
between the teres major and the teres minor, emerg-
ing at the level of the external surface of the scap-
ula. Here, at the antero-internal border of the
triceps longus and 10 mm. beyond its origin from
the axillary, the trunk bifurcates to form two
branches of approximately equal size: one of these,
the subscapular proper, passes caudad beneath the
triceps longus; the other, the external humeral cir-
cumflex, runs outward in the interval between the
triceps longus and the triceps medialis. The small
internal humeral circumflex arises from the com-
mon trunk about 5 mm. beyond the origin of the
trunk from the axillary, at the level of the internal
border of the scapula; immediately proximal to it,
and from the opposite side of the trunk, arises the
large branch supplying the latissimus, subscapu-
laris, teres major and teres minor.
The subscapular artery proper runs along the
glenoid border of the scapula for a short distance,
then divides to form two terminal branches. The
infrascapular branch of the circumflex scapular ar-
tery (cf. human anatomy) does not arise from the
circumflex scapular, but takes origin independently
from the subscapular opposite the scapular notch.
The terminal bi'anches of the subscapular are (a) a
circumflex scapular, and (b) a slightly smaller dor-
sal thoracic.
(a) A. circumflexa scapulae (fig. 134) passes
into the infraspinous fossa, where the main part of
the vessel passes aci'oss the fossa parallel to the
scapulai' spine, eventually anastomosing with the
descending branch of the transverse cervical and
the dorsal thoracic branch of the subscapular near
the gleno-vertebral angle of the scapula. A twig
from this artery enters the large infraspinous nutri-
ent foramen of the scapula; and a second twig
passes toward the spine, where it participates in
the acromial rete by anastomosing with a branch
of the transverse cervical. Immediately opposite
its origin from the subscapular, the circumflex
scapular gives off a small anastomotic branch that
passes toward the supraglenoid groove, where it
anastomoses with the infraspinous branch of the
transverse scapular.
(b) A. thoracodorsalis (fig. 134), lying between
the teres major and the triceps longus, continues
the subscapular artery along the glenoid boi'der of
the scapula nearly to the gleno-vertebral angle.
Numerous short twigs pass into the triceps longus,
and a branch arising at the ventral end of the teres
major fossa passes into the latissimus dorsi. The
vessel terminates by anastomosing with the cir-
cumflex scapular and the descending branch of the
transverse cervical near the gleno-vertebral angle.
6. A. circumflexa humeri interna [BNA:
anterior] (figs. 133, 134) is a slender vessel that
arises from the subscapular trunk just before its
terminal bifurcation. The internal circumflex di-
vides a few millimeters beyond its origin (on the
left leg these two vessels arise independently side
by side). The deeper of the two branches passes
along the ventral border of the teres minor, then
beneath the coracobrachialis, onto the head of
the humerus. Passing up across the lesser tuber-
osity and beneath the tendon of the biceps, it
anastomoses with an ascending branch of the tho-
racoacromial in the bicipital groove. The more
superficial branch of the internal humeral circum-
flex passes forward external to the coracobrachi-
alis to the proximal end of the biceps, which it
supplies; a twig supplies the coracobrachialis.
7. A. circumflexa humeri externa [BNA:
posterior] (fig. 133) is a large vessel that arises by
bifurcation of the trunk that gives rise to it and
the subscapular. The external humeral circumflex
passes ectad between the subscapularis and teres
major, emerging between the triceps medialis and
the triceps lateralis and breaking up into a number
of branches beneath the spinodeltoideus. Branches
go to both divisions of the deltoid, to the infra-
spinatus, and to the integument in the shoulder
region. Twigs from the deltoid branch enter the
acromial rete. A large descending branch supplies
the triceps medialis and the triceps longus; this
descending branch anastomoses with a branch of
the profunda brachii beneath the triceps medialis,
then bifurcates. One of the resulting twigs passes
to the olecranal rete; the other runs distad with
the lateral ramus of the superficial radial nerve, to
anastomose with an ascending twig from the dorsal
terminal branch of the volar interosseous. There
is also an anastomosis with the dorsal interosseous.
Nutrient branches enter the foramen in the head
of the humerus immediately behind the deltoid
ridge.
Brachial Artery
A. brachialis (fig. 133) is the continuation of
the axillary beyond the origin of the subscapular
trunk. There is no sharp boundary between the
brachial and median arteries, but the brachial may
be considered as terminating at the level of the
o
a.
o
T3
C
a
c
CO
6
258
DAVIS: THE GIANT PANDA
259
entepicondylar foramen, beyond which the trunk
is continued as the median. The brachial artery
runs distad along the posterior border of the bi-
ceps, and has the following relations with the
median nerve: Immediately after passing through
the loop of the median nerve, the nerve lies pos-
terior to the artery. Between this point and the
elbow the nerve makes a complete spiral revolu-
tion around the artery, so that just proximad of
the elbow it again occupies a posterior position.
The nerve and artery now diverge, the nerve con-
tinuing straight distad through the entepicondylar
foramen, while the artery follows the crease of the
elbow, lying craniad of the nerve. The artery re-
joins the nerve below the foramen, and passes
distad with it.
The brachial artery gives rise to the following
branches in addition to numerous twigs to the
flexor musculature of the upper arm: (1) the pro-
funda; (2) the superior ulnar collateral; (3) the
inferior ulnar collateral; (4) the superficial radial.
1. A. profunda brachii (fig. 133) is a small
branch arising from the posterior wall of the bra-
chial artery at the level of the bicipital arch. Im-
mediately beyond its oiigin the vessel gives off a
slender twig that follows the lower border of the
tendon of the teres major, thus lying deep to the
biceps and brachialis, to the pectoral ridge of the
humerus. Here it divides to form ascending and
descending rami that run along the pectoral ridge.
The ascending ramus anastomoses with the de-
scending ramus of the thoracoacromialis, while the
descending ramus passes down along the pectoral
ridge to anastomose with a branch of the radial
recurrent. A ramus from this twig also supplies
the coracobrachialis longus.
The main part of the pi-ofunda brachii bifurcates
about 5 mm. beyond its origin, one branch enter-
ing the medial side of the triceps longus, where it
ramifies, while the other entei-s the medial side of
the triceps medialis. A twig from the branch to
the triceps medialis accompanies the radial nerve
through the space between the triceps medialis
and triceps longus to the posterior side of the hu-
merus, where it anastomoses with the descending
ramus of the circumflexa humeri externa.
2. A. collateralis ulnaris superior (fig. 133)
arises, on the right foreleg, from the posteiior side
of the brachial about 25 mm. proximad of the in-
ternal condyle of the humerus. On the left fore
leg the two ulnar collateral arteries arise by a short
common trunk. The superior collateral crosses the
ulnar nerve, lying external to it, then accompanies
the nerve downward for a short distance before
plunging into the triceps medialis. One branch
ramifies in the distal end of the triceps medialis,
while a second passes through this muscle and into
the triceps longus, where it ramifies.
3. A. collateralis ulnaris inferior arises, on
the right leg, about 12 mm. distad of the superior
collateral. It accompanies the ulnar nerve, lying
distad of it, to the region immediately above the
internal condyle. Here the vessel breaks up to
form four main branches: (1) A slender branch runs
forward, accompanying the median nerve through
the entepicondylar foramen. (2) A branch enters
the triceps medialis, where it ramifies. (3) The
largest branch winds back behind the median epi-
condyle to the posterior side of the humerus. (4) A
slender branch accompanies N. cutaneus ante-
brachii medianus across the median epicondyle.
4. A. radialis superficialis (collateralis radi-
alis superior of veterinary anatomy) (fig. 133) arises
from the anterior side of the brachial 10 mm. be-
yond the origin of the collateralis ulnaris inferior.
At its origin it divides into a dorsal branch and a
smaller volar branch. The volar branch ramifies
extensively to the forearm flexors. The dorsal
branch runs across the distal end of the biceps,
immediately above the origin of the lacertus fibro-
sus, dividing into a pair of collateral branches at
the anterior border of the biceps; these branches
reunite at the carpus after pursuing their separate
ways down the fore arm. One of them passes
through the brachioradialis to the dorsum of the
forearm, where it joins the medial ramus of the su-
perficial radial nerve and accompanies it to the
carpus; numerous branches to the brachioradialis
considerably reduce the caliber of this vessel. The
second collateral branch joins N. cutaneus ante-
brachii lateralis and V. brachialis superficialis at
the crease of the elbow, and runs distad with them
in the groove between the pronator teres and bra-
chioradialis. The vessel winds along the distal
border of the brachioradialis onto the dorsum of
the forearm, where it receives the dorsal collateral
branch, then terminates by dividing into subequal
terminal twigs. One of these terminal twigs anas-
tomoses with the dorsal branch of the interossea
volaris, while the other opens into the anastomotic
branch of the medianoradialis, the resulting com-
mon trunk forming the radial end of the superficial
dorsal arch.
Recurrent twigs to the biceps, with a larger re-
current branch running back in the furrow between
the biceps and brachioradialis to ramify to the
latter muscle and the distal end of the clavotra-
pezius, arise from the dorsal branch before it di-
vides into its collateral branches.
The arcus dorsalis superficialis is a very deli-
cate double arch with three vessels contributing to
its formation. The first arch, which extends across
260
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
metacarpals 1 and 2, is formed by the common
trunk of the radialis superficialis and the anasto-
motic branch of the medianoradiaHs radially, and
the dorsal branch of the interossea volaris ulnar-
ward. Aa. digitales dorsales communes 12
arise from this loop. The second arch extends
across metacarpals 3 and 4, and is formed by the
dorsal branch of the interossea volaris and the ul-
naris dorsalis. It gives rise to digitales dorsales
communes 3-4. Each of these digital arteries is
joined by a delicate anastomotic branch from the
corresponding metacarpea dorsalis at the distal
ends of the metacarpal bones.
Median Artery
A. mediana communis' (fig. 133) is the con-
tinuation of the brachial beyond the level of the
entepicondylar foramen. It passes just medial of
the tendon of the biceps onto the forearm. Imme-
diately proximad of the biceps tendon it is joined
by X. medianus, which has passed through the
entepicondylar foramen. The artery and nerve
pass beneath the proximal ends of the flexor carpi
radialis and pronator teres, coming to lie in the
space between the flexor carpi radialis and the
flexor digitorum profundus. The artery lies on
the radial side of the nerve. Just proximad of the
carpus the artery divides to form two branches of
nearly equal size: the median proper and the me-
dianoradial. The first of these passes to the palm,
while the other passes around the radial border of
the wrist, deep to the tendon of the extensor pol-
licis brevis, onto the dorsum of the hand.
The common median artery gives off the follow-
ing branches on the forearm.
1. A. recurrens radialis (Davis, 1941, p. 176)
is a small branch arising from the lateral side of
the median artery at the level of the entepicondy-
lar foramen. It ascends along the humeromedial
border of the brachialis, dividing after about 15
millimeters to form two branches.
One of these branches passes back around the
distal end of the insertion tendon of the deltoid,
sending twigs to the tendon and to adjacent parts
of the brachialis; a twig passes proximad along the
medial border of the deltoid tendon, to anasto-
mose with the descending branch of the profunda
brachii. Another small twig passes from the main
trunk to the distal end of the humerus.
The other branch passes around in front of the
distal end of the humerus, beneath the brachialis.
Twigs are given off to the distal end of the bra-
> I follow the German anatomists in regarding the main
artery in the forearm as the median rather than as the
radial. Conditions found in lower mammals show that it is
erroneous to designate this vessel the radial, as Reighard
and Jennings (1935) have done.
chialis. After emerging on the opposite side of the
brachialis the vessel breaks up to form numerous
terminal twigs, which pass, in contact with the
radial nerve, to the extensor carpi radialis longus
and brevis.
2. Aa. recurrentes ulnares (fig. 133) are three
small branches arising from the medial side of the
median artery a few millimeters below the origin
of the brachialis anterior. The first of these passes
through the pronator teres, emerging on the me-
dial surface of the forearm. In addition to supply-
ing the pronator teres, it sends twigs to the flexor
carpi ulnaris, the flexor digitorum profundus, and
the palmaris longus. The second branch runs back
into the entepicondylar foramen, where it anasto-
moses with a branch of the collateralis ulnaris in-
ferior. The third branch gi-eatly exceeds the other
two in caliber, and arises 20 mm. farther distad.
Its origin is adjacent to the origin of the ulnar
artery. The vessel forms three main twigs. The
smallest passes distad to supply the condylar heads
of the flexor digitonim profundus. A second twig
passes back to the ulnar articulation, giving off
twigs to the proximal ends of the flexor muscles on
the ulnar side of the forearm. A third twig passes
to the ulnar articulation, giving off twigs to the
ulnar head of the flexor digitorum profundus, and
terminates in the olecranal region.
3. A. collateralis radialis (fig. 133) arises from
the radial side of the median opposite the origin
of the ulnar artery. It bifurcates just beyond its
origin. One twig supplies M. pronator teres. The
other passes around in front of the brachialis, to
anastomose with the recuiTent interosseous; twigs
are given off along its course to the brachialis and
the extensor carpi radialis longus.
4. Rr. musculares. Numerous short branches
pass from the median artery along its course to
contiguous muscles on the flexor side of the forearm.
5. A. ulnaris (fig. 133) is a fair-sized branch,
approximately the same diameter as the interossea
volaris, that arises from the ulnar side of the me-
dian at the level of the insertion of the biceps, i.e.,
at the proximal fifth of the forearm. It runs to
the ulnar side of the forearm, and then toward the
carpus, but remains hidden by the flexor muscula-
ture throughout its course. It gives off twigs to
the flexor muscles situated on the ulnar side of the
forearm, and thus its caliber is considerably re-
duced. Several millimeters before reaching the
pisiform, at about the distal quarter of the fore-
arm, it divides into a very slender ulnaris volaris
and a larger ulnaris doi-salis. The volaris passes
onto the palm, where it anastomoses with the
branch of the mediana propria that goes to the
outer border of digit 5; the ulnar artery has no
I
DAVIS: THE GIANT PANDA
261
connection with the superficial volar arch proper.
The ulnaris dorsalis accompanies the dorsal ramus
of the ulnar nerve onto the dorsum of the manus
just proximad of the pisiform. On the dorsum it
anastomoses with the much larger medianoradialis
to form the deep dorsal arch, and sends twigs into
the dorsal carpal rete; an additional fine twig forms
the ulnar half of the delicate superficial dorsal arch
with the dorsal branch of the interossea volaris.
The branch of the ulnaris dorsalis that goes to the
outer side of digit 5 (metacarpea dorsalis 5) gives
off an anastomotic loop that passes around the
border of the hand to anastomose with metacarpea
volaris 5.
6. Aa. interosseae. There is no interossea
communis, the volar and dorsal branches arising
together, but without the intervention of a com-
mon trunk; they come off immediately distad of
the ulnaris. A. interossea volaris (fig. 133)
slightly exceeds the dorsalis in caliber. It passes
distad on the intei'osseous membrane, accompa-
nied by its vein, to the radiocarpal articulation.
Numerous twigs are given off to the deep fiexor
muscles of the forearm, and nutrient twigs to the
ulna and radius. At the radiocarpal articulation
it divides into a large dorsal terminal branch and
a slender volar terminal branch. The volar ter-
minal branch passes between the heads of the
ulna and radius onto the carpus, where it divides;
the larger branch passes toward the pisifoi'm, where
it anastomoses with the volar branch of the ulnar
artery; the smaller branch passes toward the base
of the radial sesamoid, to anastomose with a twig
from the R. carpeus volaris of the medianoradialis.
The dorsal terminal branch perforates the in-
terosseous membrane near the base of the carpus.
On the dorsal side of the forearm it first gives off a
twig that runs proximad between the extensor digi-
torum communis and the extensor digitorum lat-
eralis, to anastomose with a descending branch of
the interossea dorsalis. The main trunk bifurcates
after giving off this twig. The more superficial
of the resulting branches runs distad external to
the dorsal carpal ligament. At the proximal bor-
der of the ligament it gives off a recurrent twig
that runs back toward the elbow beside the lateral
branch of the superficial radial nerve, to anasto-
mose with a descending branch of the external cir-
cumfiex humeral. The superficial branch divides
on the carpal ligament, one twig passing toward
the pollex to anastomose with the anastomotic
ramus of the medianoradialis to form the radial
half of the superficial dorsal arch, while the other
forms the ulnar half of this arch with a twig from
the ulnar. The deeper twig of the dorsal terminal
branch passes beneath the dorsal carpal ligament,
where it enters the dorsal carpal rete.
A. interossea dorsalis (figs. 133, 134) emerges
onto the dorsal side of the forearm by perforating
M. abductor pollicis longus. It divides immedi-
ately into two branches of approximately equal
caliber. One of these, A. interossea recurrens,
runs back toward the olecranon, giving off twigs
to the proximal ends of the extensor muscles of the
forearm and continuing into the olecranal rete.
The second branch, the main continuation of the
dorsal interosseous, runs distad beneath the ex-
tensor digitorum. It supplies twigs to the exten-
sor muscles, the largest of these anastomosing with
the descending branch of the external circumflex
humeral. The vessel terminates by emptying into
the dorsal terminal branch of the interossea volaris.
7. A. medianoradialis (figs. 133, 134) arises,
as usual in carnivores, from the bifurcation of the
common median artery, just proximad of the car-
pus. The medianoradialis is the larger of the two
resulting branches, and passes diagonally radial-
ward with N. cutaneus antibrachii lateralis.
About 25 mm. beyond its origin the mediano-
radialis gives rise to a branch, R. carpeus volaris
(fig. 133), from its medial wall. This branch runs
distad beneath the tendons of the fiexor muscles
and enters the volar carpal rete. A few milli-
meters farther distad the medianoradialis gives off
a long anastomotic ramus that accompanies N. cu-
taneus antibrachii lateralis around the radial sesa-
moid, superficial to the tendon of the abductor
pollicis longus, to the dorsum, where it receives a
delicate anastomotic twig from the brachialis super-
ficialis, then anastomoses with the dorsal branch
of the interossea volaris to form a part of the
superficial dorsal arch.
Winding up around the base of the radial sesa-
moid, deep to the tendon of M. abductor pollicis
longus, the trunk of the medianoradialis reaches
the dorsum manus, where it terminates by anasto-
mosing with the ulnaris dorsalis to form the deep
dorsal arch. Upon reaching the dorsum the me-
dianoradialis first gives off (a) a slender perforating
twig that passes between the base of the first meta-
carpal and the radial sesamoid to the vola, where
it participates in the formation of the radial end
of the deep volar arch. This is followed immedi-
ately by (b) a somewhat larger twig that passes
distad between the radial sesamoid and digit 1.
This twig divides into subequal terminal twigs,
one of which supplies the outer border of digit 1,
and the other goes to the radial sesamoid. A per-
forating twig from the latter passes to the vola
between the radial sesamoid and the first meta-
carpal, to participate in the formation of the radial
end of the deep volar arch. A second twig passes
around the outer border of the radial sesamoid.
262
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
accompanying the nerve that supplies the radial
sesamoid, and empties into the anastomotic loop
of the medianoradialis on the vola. At the distal
border of the carpus the medianoradialis gives off
(c) a twig that passes transversely across the carpo-
metacarpal articulation to anastomose with a cor-
responding twig from the ulnaris dorsalis. This
anastomotic loop gives off several twigs to the
dorsal carpal rete.
The arcus dorsalis profundus (fig. 134) is
formed by the union of the medianoradialis and
the ulnaris dorsalis. It lies deep to the extensor
tendons of the digits. From it are radiated Aa.
metacarpeae dorsales 1-4, which run to the cor-
responding intermetacarpal spaces. The second
and third dorsal metacarpals are the largest. Near
the middle of the first phalanx each dorsal meta-
carpal divides into two Aa. digitales volares
propriae, and at the bifurcation each dorsal meta-
carpal receives the perforating branches of the cor-
responding volar common digital.
In addition to the dorsal metacarpal arteries,
the deep dorsal arch gives rise to a perforating
branch that pierces the interstitium between the
second and third metacarpal bones. On the palm
it enters the middle of the deep volar arch.
The arcus volaris profundus (fig. 133) is
slightly smaller in caliber than the superficial volar
arch, and is a compound arch with contributory
vessels entering it at three points. The main source
of the arch is the large perforating branch of the
medianoradialis that passes through the second in-
termetacarpal space. On the vola this vessel di-
vides, one anastomotic loop passing across the
base of the first metacarpal to inosculate with a
common trunk formed by the union of the two
perforating twigs that pass between the radial ses-
amoid and the first metacarpal. This part of the
arch gives lise only to A. metacarpea volaris 1.
The second and larger anastomotic loop from the
perforating branch passes toward the ulnar side of
the palm, anastomosing with terminal twigs of the
mediana propria to complete the arch. This part
of the arch gives rise to Aa. metacarpeae volares
2-4. Each volar metacarpal opens into the corre-
sponding common digital artery at the distal end
of a metacarpal bone.
8. A. mediana propria (fig. 133) accompanies
the median nerve to the palm. In the wrist it gives
off a large branch to the outer side of digit 5 ; this
branch gives off a transverse anastomotic loop to
the parent vessel in the palm; it also receives the
terminus of the ulnaris volaris, and beyond the
pisiform a slender anastomotic twig from the ul-
naris dorsalis. The main trunk of the mediana
continues onto the palm, where it curves in a gen-
tle arc (arcus volaris superficialis) toward the
ulnar side. A branch to the outer side of the pollex,
which also supplies a twig to the radial sesamoid,
and Aa. digitales volares communes 1-3 arise
from the arch, while the trunk itself is continued
as the digitalis volaris communis 4. Each com-
mon digital bifurcates at the distal end of the
metacarpal bone to form two Rr. perforantes,
which pass through the interosseous spaces to anas-
tomose with the corresponding dorsal metacarpal
artery. The second, third, and fourth common
digitals receive the corresponding volar metacarpals
from the deep volar arch.
Abdominal Aorta
Parietal Rami
A. phrenica anterior (fig. 135) arises from the
left ventral wall of the aorta as the latter passes
between the medial crura of the diaphragm. Its
origin is 12 mm. anterior to the origin of the celiac
axis. The vessel divides into right and left branches
25 mm. beyond its origin; the right branch is some-
what smaller than the left (see below under Renal
Arteries). A small left posterior phrenic arises
from the base of the anterior phrenic. The right
posterior phrenic comes from the right renal artery.
Celiac Artery
A. coeliaca (fig. 135) arises from the ventral
wall of the aorta immediately after the latter
emerges from the diaphragm, i.e., ventrad of the
last thoracic vertebra. The celiac artery is a short
vessel which passes forward and slightly to the left
for about 12 mm., then breaks up to form three
branches: the hepatic, the splenic, and the left
gastric arteries.
1. A. hepatica arises independently from the
ventral wall of the celiac artery. It is only slightly
smaller than the splenic artery, but much larger
than the left gastric. It passes forward alongside
the portal vein to the liver, giving off a single large
branch (the gastroduodenal). Near the liver the
hepatic artery divides into the customary right
and left branches, which supply the liver and gall
bladder.
A. gastroduodenalis is very short, dividing
about 5 mm. beyond its oi'igin from the hepatic
artery to form two branches of nearly equal size.
The larger of these is a short trunk which forks
after 9 mm. to form the right gastroepiploic and
anterior pancreaticoduodenal arteries. A. gas-
troepiploica dextra runs beneath the duodenum,
turns to the left and runs along the pylorus (in the
omentum), to anastomose with the left gastroepi-
ploic branch of the splenic near the proximal end
of the pylorus. The usual twigs are given off to
Hiatus aorticiis
A. hepatica
Gl. sttprarenales
Diaphragma
\ phrenica '\nt
A,o?t I ihdominalis
\ plirenita p(t.
\ dastrua sin.
Vena cava post
V. phrenica access. ^
A. phrenica post.
\AVrenaIis dext,
"^alyx ren. maj
Ren dext.
Rennilu.< ^
Hilus _m<M
Cortex ^^^5^
Medulla ^""^^S
Papiila
Pelris renalia
Tunica fibrosa
Calyces ren. min
M.quad. lum^'^'M
V. lumbalis con ^^
Ri (K'sopliajjei
ii,..^. lienalis
.\. eoeliaca
Tendo diaphr.
M. psoas maj-
A. mesenterica
post
M. iliacus
A. & V. lumbalis
rA.&V. spormatica
interna
M.lran.-iversus
al)d()ininis
M.ol)li<iuus
intern us
( 'refer
M. psoas mm
A.&V.circ. ilium pr fV
R. iliacus lat ^
R. m. sartonui.
R. lumbalis
A. hypogast. panetalis
V. hypogastrica
A. & V. iliolumbalis'^
A. sacral is lateralis
A. & V. femoris
A. & V. Klutea ant.
A. & V. haemorrhoid. med
A. & v. circ. ilium superf.
A. & \'. profunda femoris
I'reler (cut)-
M. cremast.
Tunica raffinalis com.
Tun. rag. prop., lamina parietalis
Ductus deferens {cut
Caput epididymis
Tun. rag. prop., lamina rviceralis
Corpus epididymis
Testis
Fascia cremasteric a
Septtda testis
Cauda epididifmis
Fascia m. red. abdom
.\. & V. iliaca externa
A. hypogast. vi.sceralis
Peritonaeum {cut)
Textus adiposus
Ductus deferens
A. umbilicalis
Funiculus spermaticus
A. & y. sacralis media
A. pudenda int.
A. & V. epigastrica post.
R. pubicus
-Tr. pudcndo-epigast. (cut)
A. & V. haemorrhoid. ant.
.\. & V. epigastrica superf.
A. & \'. spermatica ext.
M. rectus abdominis (cut)
Cutis (cui_
Praeputium
Fig. 135. Vessels and nerves of the abdomen of Ailuropoda
263
Tunica vaginalis com.
Gubernaculum testis
R. anast. a. pudenda ext.
Corpus penis
Clans penis
Orificuim urethrae ext.
264
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
the pylorus and omentum. A, pancreaticoduo-
denalis anterior runs through the substance of
the head of the pancreas, giving off twigs to the
pancreas and duodenum, and anastomosing with
the posterior pancreaticoduodenal artery near the
caudal end of the duodenum.
The smaller branch of the gastroduodenal artery,
A. gastrica dextra, is more important as a blood
supply to the corpus of the pancreas than to the
stomach. A branch (the right gastric proper) runs
through the lesser omentum, giving off twigs to the
pylorus and eventually anastomosing with the left
gastric in the lesser curvature of the stomach.
2. A. lienalis is the largest branch of the celiac
artery. After giving off the hepatic artery, the
celiac continues for 3 or 4 mm. and then divides
to form the splenic and left gastric arteries. A. lien-
alis follows the curvature of the gastrolienal liga-
ment. Two pancreatic branches arise from the
proximal end of the artery and supply the cauda
and coi-pus of the pancreas, also giving off epiploic
twigs to the omentum. Large splenic branches,
which become progressively smaller and shorter
toward the posterior end of the spleen, are given
off from the main trunk of the artery at more or
less regular intervals. In the region of the fundus
of the stomach each splenic branch divides into at
least two twigs near its terminus, one of which goes
to the spleen while the other (the vasa brevia of
human anatomy) passes in the omentum to the
wall of the stomach. Near the posterior end of the
spleen the gastric and splenic twigs are independ-
ent, coming off from opposite sides of the main
trunk. The main trunk is continued as the A. gas-
troepiploica sinistra, which lams in the omentum
along the pylorus to anastomose with the right
gastroepiploic artery.
3. A. gastrica sinistra is the smallest branch
of the celiac artery. It follows the lesser curvature
of the stomach, giving off numerous twigs to the
cardia. A separate anastomotic branch arises high
on the cardia and runs through the lesser omentimi
to join the right gastric which runs along the py-
lorus from the opposite direction. At its base the
left gastric gives rise to two small branches, the
Rr. oesophagi. The more medial of these runs
craniad just to the left of the midline, dividing into
right and left branches at the level of the eso-
phageal opening in the diaphragm. The other
ramus runs craniad, supplying the posterior end
of the esophagus.
Anterior Mesenteric Artery
A. mesenterica anterior arises from the ven-
tral wall of the aorta about 15 mm. caudad of the
celiac artery (fig. 135). It slightly exceeds the
celiac in size. It runs through the mesentery in a
short, sharp arc, giving off the following branches:
(1) the posterior pancreaticoduodenal; (2) the intes-
tinal arteries; and (3) the ileocolic trunk (fig. 113).
1. A. pancreaticoduodenalis posterior arises
from the anterior wall of the anterior mesenteric
about 25 mm. beyond the origin of the latter from
the aorta, i.e., as the anterior mesenteric passes the
edge of the pancreas. Running into the head of
the pancreas, it supplies that region and the poste-
rior end of the duodenum, anastomosing with the
anterior pancreaticoduodenal within the substance
of the pancreas.
2. Aa. intestinales arise from the convex side
of the arch of the anterior mesenteric and radiate
into the mesentery in the usual way. Nine main
branches come off from the arch, and each of these
bifurcates a few millimeters beyond its origin. The
primary loops so formed are further subdivided
down to quinary divisions. Near the intestinal
border of the mesentery the usual inosculations
join the separate branches to one another. The
termination of the arch of the anterior mesenteric
forms a strong anastomosis with a branch of the
ileocolic artery. Twigs from the main branches
before their bifurcation supply the large lymph
gland (pancreas of Asellus) which lies dorsad of
the arch of the anterior mesenteric.
3. The Truncus ileocolicus is the first artery
that arises from the anterior mesenteric; it comes
off several millimeters before the posterior pancre-
aticoduodenal, and from the opposite side of the
mesenteric artery. The Aa. ileocolicae and col-
icae take origin from this trunk. Two ileocolic
arteries arise from the ileocolic trunk, and the
trunk itself is continued as a third. The latter,
which is the largest ileocolic branch, anastomoses
with the termination of the anterior mesenteric
artery.
The anterior and middle colic arteries arise from
the ileocolic trunk near its origin from the mesen-
teric artery. A. colica anterior [BNA: colica
dextra] comes off first, followed a millimeter or
two farther distad by the A. colica media. The
anterior colic divides into anterior and posterior
branches near the intestinal wall. The anterior
branch supplies the proximal end of the colon by
means of numerous short intestinal twigs and con-
tinues craniad to anastomose with the first branch
of the ileocolic artery; the posterior branch like-
wise gives off intestinal twigs and continues caudad
to anastomose with the anterior branch of the mid-
dle colic. The middle colic divides into anterior
and posterior branches, each of which sends nu-
merous short branches to the colon. The anterior
branch, as noted above, anastomoses with the an-
DAVIS: THE GIANT PANDA
265
terior colic; the posterior branch runs caudad and
anastomoses with the posterior coHc.
Renal Arteries
Aa. renales (fig. 135) arise symmetrically from
the lateral walls of the aorta, 20 mm. caudad of the
anterior mesenteric, i.e., at the level of the first
lumbar vertebra. Each passes almost straight lat-
erad across the crus of the diaphragm to the hilus
of the kidney. In the hilus it breaks up into three
branches, which in turn ramify to the individual
lobules. The renal artery gives off the following
branches in addition to the main trunk supplying
the kidney:
1. A. lumboabdominalis is a large vessel aris-
ing from the anterior wall of the renal immediately
beyond the origin of the latter from the aorta. The
right lumboabdominal passes dorsad of the corre-
sponding vein, whereas the left passes ventrad.
On the left side the A. suprarenalis posterior
arises as the vessel passes the suprarenal body, and
runs forward to the posterior end of that organ ; on
the right side the lumboabdominal gives rise to the
right posterior phrenic, and the right posterior
suprarenal comes from this. The lumboabdom-
inal runs diagonally backward and outward along
the dorsal body wall.
2. A. suprarenalis anterior arises on the left
side of the body from the anterior wall of the renal
beyond the origin of the lumboabdominal. On the
right side it is a short lateral branch from the ac-
cessory phrenic as the latter vessel passes the supra-
renal body.
3. A. phrenica accessoria. An accessory
phrenic branch arises from the anterior wall of the
right renal artery slightly laterad of the middle of
the renal. It passes forward and outward, ventrad
of the suprarenal body, across the crus of the dia-
phragm, supplying the dorsal part of the right half
of the diaphragm. A similar, but much smaller
vessel arising from the left renal does not reach the
diaphragm, but loses itself in the fat surrounding
the kidney.
Internal Spermatic Arteries
Aa. spermatica internae (fig. 135) arise from
the lateral wall of the aorta 20 mm. caudad of the
renal artery. The two arteries are given off sym-
metrically. Each passes diagonally backward and
outward to the abdominal inguinal ring, where it
is joined by the ductus deferens. At about one-
third the distance between its origin and the in-
guinal ring each spermatic gives rise to a lateral
branch that passes to a prominent mass of post-
renal fat. Beyond this point the spermatic artery
breaks up to form a rete mirabile, which is main-
tained distad into the epididymus.
Posterior Mesenteric Artery
A. mesenterica posterior (figs. 113, 135) arises
from the ventral wall of the aorta at the level of
the third lumbar vertebra, 40 mm. behind the ori-
gin of the internal spermatics and 45 mm. in front
of the posterior end of the aorta. The vessel passes
caudad and toward the colon within the mesocolon.
Near the colon it gives rise to the small A. colica
posterior, which passes craniad, giving off numer-
ous twigs to the posterior part of the colon, to
anastomose with the middle colic. The main part
of the posterior mesenteric is continued caudad as
A. haemorrhoidalis anterior, which ramifies
over the anterior part of the rectum, anastomos-
ing posteriorly with the middle hemorrhoidal.
Terminal Branches of the Aorta
The aorta terminates abruptly at the level of the
posterior border of the fourth lumbar vertebra by
breaking up to form two paired vessels and one
unpaired vessel. The first and largest of the paired
vessels are the external iliacs. The much smaller
hypogastrics diverge symmetrically from the mid-
line immediately behind the external iliacs. Thus
the continuation of the aorta as a common trunk
before the hypogastrics are given off (the so-called
hypogastric trunk) is scarcely represented in Ailu-
ropoda. Dorsad of the origin of the hypogastrics
the much reduced aorta is continued into the tail
as the middle sacral artery.
Hypogastric Artery and Its Branches
Aa. hypogastricae arise from the bifurcation
of the external iliacs with scarcely an indication of
a hypogastric trunk (fig. 136). Each divides al-
most immediately to form a parietal and a visceral
ramus, and these pass caudad, the parietal ramus ly-
ing above and a little to the outside of the visceral.
The parietal branch divides at the level of the
second sacral foramen into the anterior gluteal ar-
tery and the very slender lateral sacral.
1. A. glutaea anterior (figs. 136, 138) emerges
from the pelvis at the anterior border of M. piri-
formis (i.e., at the extreme anterior end of the gi-eat
sciatic foramen), accompanied by the anterior glu-
teal nerve. It then breaks up into several terminal
branches, which ramify to the gluteal muscles and
the piriformis. A branch descends toward the tro-
chanteric rete, sending an anastomotic twig to the
posterior gluteal artery and participating in the for-
mation of the rete.
2. A. caudae sacralis lateralis passes into the
tail, where it lies in the groove between the dorsal
and ventral sacro-coccygeal muscles.
The visceral branch of the hypogastric gives rise
to the following vessels:
266
FIELDIAXA: ZOOLOGY MEMOIRS, VOLUME 3
A. fern
A. epigasthca post.
R. deferentialis,
A. sacralisjat
A. spcnnatica externa
Ir.ctsura ischiadica major
Spina ischiadica
Incisura iachiadica minor
Lig. ingiiinalis (cut)
A. glutea ant.
A. prof. fem.
Ductus deferens
A. sacralis media
A. iliaca ext- (cut)
Aa. lumbales
.A. spermatica int
abdominalis
Vesica urinaria
Urachus ' lig. umb. med.)
A. haemorrhoid. med.
A. vesica post.
Fig. 136. Terminal branches of the abdominal aorta in Ailuropoda.
1. A. umbilicalis (fig. 136) is given off from
its lateral wall 20 mm. beyond the origin of the
artery itself, and passes back to the bladder. As
it nears the bladder the vessel gives off A. vesi-
calis anterior, which ramifies over the anterior
part of the bladder. The umbilical artery then
ceases to be pervious, and passes around onto the
ventral side of the bladder, from where it continues
craniad in the lateral lunbilical fold as the lateral
umbilical ligament.
2. A. vesicalis posterior (fig. 136) arises from
a tnmk common to it and the middle hemor-
rhoidal. It passes onto the posterior part of the
dorsum of the bladder, where it ramifies. A fine
twig runs caudad on the ureter, and a posterior
twig anastomoses with a twig from the middle
hemorrhoidal.
3. A. haemorrhoidalis media (figs. 135, 136)
passes caudad and ventrad to the middle part of
the rectum, over which it ramifies. Branches go
to the urethra, to the ampulla of the ductus def-
erens, and to the muscles surrounding the rectum.
Anteriorly it anastomoses with the anterior hemor-
rhoidal, and posteriorly with the posterior hem-
orrhoidal arteries.
4. A. glutaea posterior (fig. 138) is of the same
caliber as the internal pudendal, so that the tnmk
appears to bifurcate to form these two terminal
vessels. The posterior gluteal emerges from the
pelvis just behind the sciatic nerve, at the poste-
rior border of M. piriformis, and immediately
breaks up into terminal branches. These supply
the posterior part of the gluteus superficialis, the
obturator internus, and the gemelli, and partici-
pate in the formation of the trochanteric rete. The
branch ninning to the rete anastomoses with the
circumflexa femoris medialis. A posterior branch
anastomoses with a terminal branch of the pro-
funda at the ischial tuberosity. A. comitans n.
ischiadici is absent.
5. A. pudenda interna is the second of the
terminal vessels of the visceral division of the hj^po-
gastric. It nms caudad beside the rectiun, divid-
ing near the posterior border of the ischium into
the artery of the penis and a trunk for the posterior
hemorrhoidal and perineal arteries, (a) A. peri-
naei bifurcates at its origin. One branch descends
vertically, external to M. levator ani and in front of
M. sphincter ani externus, to the base of the penis.
DAVIS: THE GIANT PANDA
267
giving twigs to the ventral part of the anus and
to Mm. ischiocavernosus, bulbocavernosus, and
levator penis. The other branch runs caudad, sup-
plying the skin around the dorsal and lateral parts
of the anus, (b) A. haemorrhoidalis posterior
runs to the anal region, where it ramifies richly in
the skin surrounding the anus. A single twig goes
to the terminal part of the rectum, (c) A. penis
arises from the ventral wall of the internal puden-
dal 20 mm. before its termination. It descends
vertically to the base of the penis, where it breaks
up to form three vessels: the artery of the bulb,
and the deep and dorsal arteries of the penis. A.
bulbi urethrae is a slender branch that runs cra-
niad to ramify over the bulbus urethrae, anasto-
mosing anteriorly with a twig from the middle
hemorrhoidal. A. profunda penis is a short
branch that enters the crus penis. A. dorsalis
penis passes onto the dorsum of the penis, first
giving off a delicate twig to the bulbus urethrae;
the main trunk runs along the penis to the glans,
where it anastomoses with twigs from the external
pudendal and with its mate from the opposite side.
External Iliac Artery and Its Branches
A. iliaca externa (fig. 135) passes diagonally
caudad from the aorta across the ventral surface
of M. psoas minor, to the femoral ring. Passing
through the ring onto the medial surface of the
thigh, it lies in the femoral triangle and takes the
name of femoral artery. The external iliac artery
lies ventrad of the corresponding vein, and has a
length of 100 mm. It gives rise to the following
branches: (1) the deep circumflex iliac, (2) the ilio-
lumbar, and (3) the deep femoral.
1. A. circumflexa ilium profunda (fig. 135)
arises asymmetrically on the two sides of the body.
On the left side it comes off at the very base of the
external iliac, while on the right it arises from
the external iliac 20 mm. beyond the origin of the
latter. The vessel passes deep to the common iliac
vein, running laterad and slightly caudad across
the dorsal body wall. Twigs from its posterior
wall pass into the iliacus and psoas, supplying
these muscles and anastomosing with a branch
from the iliolumbalis within the muscle tissue.
Just before reaching the iliac crest it gives off a
branch that pierces the body wall to supply the
proximal end of M. sartorius. At the level of the
iliac crest the main vessel pierces M. transversus,
bifurcating immediately to form anterior and pos-
terior branches that ramify between this muscle
and M. obliquus internus. The anterior branch
anastomoses with a muscular branch of the lum-
bar arteries; the posterior branch anastomoses with
the superficial circumflex iliac.
2. A. iliolumbalis (fig. 135) arises from the
dorsomedial wall just proximad of the deep fe-
moral. It passes dorsad around the external iliac
vein and the tendon of the psoas minor, giving off
the following branches: (1) A twig arises from its
posterior wall 10 mm. beyond its origin and runs
back into the pelvic cavity, where it anastomoses
with the obturator twig of the profunda femoris.
(2) R. lumbalis is a small twig given off from the
opposite side and just distad of the preceding. It
breaks up in the psoas minor. The main vessel
continues as the (3) R. iliacus, which passes lat-
erad across iliopsoas muscles. It gives off several
nutrient branches to the body of the ilium and
muscular twigs to the iliopsoas muscles. About
midway across the psoas major the vessel breaks
up to form terminal branches. In addition to mus-
cular branches that supply the gluteus medius
and minimus, anastomotic branches run forward
to the deep circumflex iliac and the last lumbar.
3. A. profunda femoris' (figs. 135-137) arises
from the medial wall 40 mm. before the external
iliac reaches the femoral ring. It diverges from
the external iliac, running almost parallel with the
longitudinal axis of the body. It passes through
the femoral ring onto the medial side of the thigh,
where it lies beneath M. pectineus and in contact
with the ventral surface of the ilium just caudad of
the iliopectineal eminence. Continuing caudad
beneath M. adductor femoris and adductor longus,
i.e., across the juncture between the ilium and
pubis and across the articular capsule of the hip
joint, it reaches the posterior side of the thigh.
Here, between the adductor femoris and the quad-
ratus femoris, it breaks up to supply the posterior
thigh musculature.
The deep femoral artery gives rise to the follow-
ing branches:
(a) Truncus pudendo-epigastricus (fig. 135)
arises from the ventral wall of the deep femoral at
the internal inguinal ring. It divides 10 mm. be-
yond its origin into the posterior epigastric and
external spermatic arteries. A. epigastrica pos-
terior is the larger of the two branches and runs
craniad. It gives off' a fine twig that supplies the
extreme posterior end of M. rectus abdominis, then
continues through the suspensory ligament of the
bladder to the neck of the bladder. The main
trunk of the posterior epigastric gives off a branch
to the rectus abdominis, then enters the space be-
' The origin of the deep femoral has migrated up inside
the inguinal ligament in carnivores, so that in these animals
it corresponds to A. obturatoria+A. profunda femoris
of human anatomy. The origin of A. circumflexa femoris
lateralis has been transferred from the deep femoral (as
it is in man) to the femoral. The deep femoral is absent in
Procyon loior and some bears (Zuckerkandl, 1907).
268
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
tween M. transversus and M. obliquus internus,
sending off a fine anastomotic branch to the super-
ficial epigast!-ic; branches ramify over both these
muscles and to the rectus. The anterior ends of the
vessel anastomose with the superficial and anterior
epigastrics. A. spermatica externa runs along
the medial border of the spermatic cord to the
testis, where it divides. The smaller of the two
resulting branches sends twigs into the tissues sur-
rounding the testis and into the skin of the scrotal
region, in addition to a twig that enters the prepuce,
where it anastomoses with the external pudendal.
The other branch of the external spermatic repre-
sents A. epigastrica superficialis. It divides in
the subcutanea of the inguinal region, the smaller
branch running distad on the medial surface of the
thigh, while the other runs craniad in the subcuta-
neous fat over the rectus abdominis, to anastomose
with a branch of the posterior epigastric.
(b) R. nutritius is a slender branch arising
from its anterior wall just outside the abdominal
wall. It passes to the region of the ilium just
craniad of the acetabulum.
(c) Rr. musculares pass to the posterior thigh
muscles. The first of two large muscular rami aris-
ing from the posterior wall of the profunda near its
proximal end sends a twig through the obturator
foramen. This twig, which apparently represents
the obturator artery of human anatomy, gives off
pubic, anterior, posterior, and acetabular branches.
(d) A. circumflexa femoris medialis is repre-
sented by two branches. A slender branch arising
from the medial wall of the profunda at the level
of the first muscular ramus apparently represents
R. superficialis; it supplies the pectineus and ad-
ductor brevis and sends a fine twig to the gracilis.
R. profunda arises from the anterior wall of the
profunda near the posterior border of the pec-
tineus, passes between the adductor magnus and
the obturator externus, and divides into ascending
and descending branches on the external surface
of the thigh. The ascending branch participates
in the trochanteric rete and anastomoses with the
posterior gluteal; the descending branch passes
down along the posterior border of the vastus lat-
eralis, anastomosing with the ascending perforat-
ing branch of the femoral.
(e) One of the terminal branches of the pro-
funda passes ectad between the quadratus femoris
and semimembranosus and divides into ascend-
ing and descending rami on the external surface
of the thigh. The ascending branch breaks up at
the ischial tuberosity to form muscular twigs and
an anastomotic twig that joins the posterior glu-
teal; the descending branch runs distad behind the
sciatic nerve, giving off twigs to the posterior thigh
musculature.
(f) A. pudenda externa (fig. 137) is a slender
twig from the medial terminal branch of the pro-
funda. It runs mesad to the posterior border of
the ascending ramus of the pubis, along which it
descends to the penis. Entering the ventral wall
of the prepuce, it ramifies in the prepuce, anasto-
mosing with its mate from the opposite side and
with the pudendal branch of the external spermatic.
Femoral Artery
A. femoralis (figs. 136, 137) is the continuation
of the external iliac beyond the femoral ring. It lies
anterior to the femoral vein, passing first through
the femoral triangle, then deep to the adductor fe-
moris and semimembranosus. Finally it emerges
into the popliteal space through the interval be-
tween the anterior and posterior parts of the ad-
ductor longus and magnus (there is no tendinous
opening), where it becomes the popliteal artery.
It gives rise to the following branches.
(1) A. circumfiexa ilium superficialis (fig. 137)
arises from the posterior wall of the femoral just
beyond the inguinal ligament. It passes back
through the femoral ring, then runs craniad on
the internal abdominal wall, to anastomose with
a descending branch of the deep circumflex iliac.
Rr. inguinales arise from the superficial circum-
flex iliac near its base. They run back toward the
inguinal ring, to ramify in the transverse and in-
ternal oblique muscles in the inguinal region. The
most anterior twig anastomoses with a descending
twig of the anterior epigastric.
(2) A. circumflexa femoris lateralis' (fig. 137)
is by far the largest branch of the femoral. It is a
short trunk arising from the anterior wall of the
femoral 25 mm. beyond the inguinal ligament.
The trunk runs toward the anterior side of the
thigh, bifurcating 10 mm. beyond its origin to form
two branches of approximately equal size. R. an-
terior promptly bifurcates again. One resulting
branch runs craniad and distad beneath the sar-
torius and tensor fasciae latae, passing between the
branches of the femoral nerve, and giving off twigs
to both these muscles. The other branch runs dis-
tad in the rectus femoris almost to the knee, giv-
ing off numerous twigs to that muscle and a twig
to the tensor fasciae latae. R. posterior also bi-
furcates immediately. One bi'anch passes ectad
between the rectus femoris and the vastus medialis
to the external surface of the thigh, where it gives
off twigs to the gluteal muscles and sends a de-
scending twig down along the boundary between
> See note, p. 267.
R. ciro. ilium priif.
M. obliquus iiil.
M. teiixur fasriae liifae
X. fi'mi>ralis.
R. cutaneus latonilis
R. asc'.. a. circ. fern. lat.
A. I'irc. fern, lat.
R. desc. a. circ. fern, lat
A. perforana fr. prof.fom.
A. feinoral
M.traHSversalis abd.
M. iliopsoas
Rr. inKuinalfS
M. ms7((.v Idteralii
A. circ. ilium .sup.
.M. pectineus
A. profunda fcmoris
Ox pubU
miYH -W. aiMiirlor
X. obturatorius
M. luhluctor
^^^^^_.V/. pectineus
M.^racHis
(cult
M. mlthietor
M. rertuH frmnri^. - .
A. genu supr
R. muscularii
R. articular
\. pudenda e.\t.
.V. (inadratus Jtmoritt
R. tuber, isch.
M. scininienihratioKiis
A. genu sup.
med.
, A. saphena, r. dorsalis
_A. saphena, r. plantaris
Rr. cutanei cruris medialis
N. cutaneus
Fig. 137. Vessels and nerves of thigh of Ailuropoda, medial view.
269
270
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
the rectus femoris and the vastus laterahs that
supplies these muscles; the twig to the vastus lat-
eralis anastomoses with an ascending twig of the
superior lateral genicular. The other branch of
the posterior- ramus runs toward the knee between
the rectus femoris and the vastus lateralis, supply-
ing twigs to these muscles and to the vastus inter-
medius.
(3) Rr. musculares arise from both sides of the
femoral in its course along the thigh. These supply
the sartorius, the gracilis, the rectus, the pectineus,
the vastus medialis, the vastus intermedius, and
the adductors. A posterior branch arising at about
the middle of the thigh and an anterior branch aris-
ing a few millimeters farther distad are much larger
and more elaborate than the others. The anterior
branch sends a twig to the arterial rete at the knee.
(4) A. genu suprema (fig. 137) arises from the
posteromedial wall of the femoral just before the
latter passes beneath the adductor femoris. It
breaks up after a few millimeters to form the usual
terminal branches, (a) R. articularis is the small-
est branch. It passes to the articular rete at the
knee, (b) A. saphena accompanies the saphenous
nerve distad. At the level of the medial epicon-
dyle of the femur it divides to form dorsal and
plantar branches. The larger dorsal branch ac-
companies the saphenous nerve to the dorsum of
the foot, where it anastomoses with the superficial
branch of the anterior tibial artery to form the
delicate superficial dorsal arch. From this, the
Arcus dorsalis superficialis, four fine superficial
dorsal metatarsal arteries radiate. These anasto-
mose with the corresponding deep dorsal meta-
tarsal arteries at the metatarso-phalangeal ai'ticu-
lations, to form the common digital arteries. The
plantar branch passes down the back of the leg in
the fascia; below the ventral border of the semi-
membranosus it lies in the groove for the tibial
nerve. At the bifurcation of the tibial nerve, at
the distal quarter of the leg, it anastomoses with
the superficial branch of the posterior tibial artery.
Both the dorsal and plantar branches give off nu-
merous muscular rami to the muscles along their
courses, (c) R. muscularis is the largest branch
of the genu suprema. It passes caudad across the
adductor longus, to supply the posterior thigh
muscles.
(5) A. perforans is a small vessel arising from
the femoral just before it reaches the popliteal
space. It passes back through M. adductor mag-
nus, along the posterior border of M. vastus later-
alis and beneath M. biceps, to the region of the
great trochanter. Here it anastomoses with the
descending twig of the deep branch of the circum-
flexa femoris medialis, and participates in the tro-
chanteric rete.
(6) A. poplitea (fig. 138) is the continuation of
the femoral artery in the popliteal space. It is a
very short trunk, dividing near the upper border
of the femoral condyles, some distance above the
popliteal muscle, into the anterior and posterior
tibial arteries.' The only branch arising from the
popliteal is a muscular ramus to the biceps femoris
and tenuissimus.
Anterior Tibial Artery
A. tibialis anterior (figs. 138, 139) is much the
larger of the two tibial arteries. It passes deep to
the popliteal muscle, then between the tibia and
fibula at the extreme proximal end of the interos-
seous space, and runs distad on the anterolateral
aspect of the leg, lying between the anterior mus-
cles, as far as the ankle. Beyond the tibio-tarsal
articulation it continues as the dorsalis pedis artery.
The anterior tibial gives rise to the following
branches:
(1) A. genu superior lateralis (fig. 138), the
larger of the two superior genicular branches, arises
from the anterior tibial at its base. It passes lat-
erad above the lateral condyle of the femur. An
ascending branch enters the vastus latei'alis, within
which it anastomoses with a descending branch of
the lateral circumfiex. A descending branch en-
ters into the deep articular rete.
(2) A very large muscular branch to the biceps
and tenuissimus comes off behind and slightly be-
low the superior lateral genicular. A subfascial
twig descends across the biceps, to anastomose with
the sural artery at the lower border of the biceps.
(3) A. genu inferior lateralis (fig. 138) arises
13 mm. beyond the origin of the superior lateral
genicular. It runs laterad across the lateral con-
dyle of the femur and the tendon of the lateral
head of the gastrocnemius. Only one of the four
main branches into which the vessel breaks up
passes beneath the fibular collateral ligament; the
other three pass superficial to it. Twigs from the
vessel participate in the deep articular rete, and a
descending twig runs down beneath the peroneus
longus, to anastomose with the tibial recurrent
artery.
(4) A. recurrens tibialis is represented by two
small branches arising from the anterior tibial im-
mediately after it has passed through the interos-
seous space. They run back toward the knee, lying
' The term "popliteal" for the distal end of the femoral
artery is retained here only for convenience. Because of its
division into the tibial arteries in the proximal part of the
popliteal space, the popliteal artery gives rise to none of
the branches that characterize this artery in man. Many
anatomists have attempted to circumvent this difficulty by
calling the proximal ends of the anterior and posterior tibials
the "deep" and "superficial" popliteals.
Fa>via lumhiidorsalis isufH'Tf.)_
Fascia titmlnxlursalis ifirof.).
A. & N'. glutaeus ant.
A/. giulaei4s Kuperf. icut)
M. piriformis icul
Ftiscia glulaea
Spina iliaea aul. sup.
M. glutaam nifditts inU)
M. tensor Jascuxe lata* [cut)
M. glulaeus sitperf. {aU^
A. & N.gluUeus post.
N. to m. quadralus
ft-niDris
N. cutaneus femuris [xist.
-W. gritirllt
M. oUunilor til
Br. of A. circ. fern, lat.?
^f. gliitaeus sufterf. tcul)
.\t. qiuitiratus femoris
A. perf(rana ascendens (A. femoralis)
N. tibialis
\. peroneus communis
,A. poplitea
A prof. fern. .r. ttTtniMal;
genu superior lat.
A. genu inf. lat.
M. biceps fe maris (eul)
Rr. n. cutaneus
surae lateralis)
N. articularis
recurrens
M. gai^lrocnemiuj!
i caput lateralt)
.V. tenuissimn.'? tcul)
Fig. 138. Vessels and nerves of thigh of Ailuropoda. lateral view.
271
272
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
close to the bone beneath the leg muscles, and sup-
ply structures in that region. Nutrient twigs to
the proximal ends of the tibia and fibula are in-
cluded.
(5) A. peronaea (fig. 139) is a slender branch,
no larger than the several muscle branches with
which it is associated, that arises from the anterior
tibial at its proximal third. It passes immediately
into M. peroneus brevis, running in the substance
of this muscle down to the distal third of the leg,
and winding around with the muscle to the poste-
rior side of the fibula. Here it joins the perforating
branch (8) of the anterior tibial, and the trunk so
formed runs distally between the flexor hallucis
longus and the peroneus brevis, receiving the sural
artery at the tip of the calcaneum, to form the
external end of the deep plantar arch.
(6) Rr. musculares arise from both sides of the
anterior tibial as it passes toward the foot, and
supply the surrounding musculatui-e.
(7) A. tibialis anterior superficialis (A. n.
peronei superficialis, Zuckerkandl) (fig. 139) is an
extremely slender vessel arising at about the junc-
tion of the middle and lower thirds of the leg. It
joins the superficial peroneal nerve and runs with
it between the peroneus longus and extensor digi-
torum longus onto the dorsum of the foot. Here
it anastomoses with the dorsal branch of the saphe-
nous artery to form the superficial dorsal arch.
(8) R. perforans (fig. 139) is a stout branch
coming from the posterior wall of the anterior tib-
ial just above the tibiofibular syndesmosis. It
winds around the extensor hallucis longus, per-
forates the distal end of the interosseous mem-
brane, and is joined by the peroneal artery. The
resulting trunk anastomoses with the suralis at
the tip of the calcaneum. The perforating ramus
represents the perforating section of the primitive
interosseous artery.
Just before entering the interosseous membrane
the perforating branch gives rise to a short trunk
that divides to form the medial and lateral ante-
rior malleolar arteries. A. malleolaris anterior
medialis (fig. 139) is the larger of the two malleo-
lar arteries. It runs across the medial malleolus,
giving off a nutrient twig to the tibia, to the medial
malleolar rete. The rete is formed by a twig from
the deep plantar branch of the posterior tibial and
twigs from the medial tarsal artery, in addition to
the malleolar branch. A. malleolaris anterior
lateralis (fig. 139) runs around the lateral malleo-
lus to the lateral malleolar rete. This rete is formed
by interanastomosis between this vessel and twigs
from the lateral tarsal artery.
Immediately after passing through the interos-
seous membrane, the perforating branch gives off
a nutrient twig to the distal end of the fibula. One
of the terminal twigs of the perforating branch
forms the lateral end of the superficial plantar arch
by anastomosing with the terminus of the super-
ficial branch of the posterior tibial.
Dorsal Artery of the Foot
A. dorsalis pedis (fig. 139) is the direct continu-
ation of the anterior tibial. It divides at the sec-
ond interosseous space into a branch forming the
deep dorsal arch and a much larger perforating
branch that joins the lateral tarsal artery to form
the deep plantar arch. The dorsalis pedis gives
rise to the following branches:
(1) A. tarsea medialis (fig. 139), the larger of
the two tarsal branches, arises at the same level as
the lateral tarsal, at the tibio-tarsal articulation.
It ramifies over the medial side of the tarsus, par-
ticipates in the medial malleolar rete, and sends a
twig around onto the sole to anastomose with a
twig from the first deep plantar metatarsal artery.
The main trunk of the artery runs around the me-
dial border of the tarsus, to anastomose with the
deep branch of the posterior tibial artery.
(2) A. tarsea lateralis (fig. 139) runs across the
tarsus to its lateral side, where it ramifies. It par-
ticipates in the lateral malleolar rete and the dorsal
pedal rete, anastomoses with a descending branch
of the sural artery, with the arcuate artery to form
the deep dorsal arch, and forms the lateral end of
the plantar arch. A twig arising from the lateral
tarsal near its base runs into the tarsus between
the astragalus and the calcaneum, ramifying as a
nutrient artery of the tarsus.
(3) A. metatarsea dorsalis 1 arises from the
dorsalis pedis just proximad of the tarso-metatar-
sal articulation. At the base of the first meta-
tarsal it breaks up into a perforating branch that
passes through the first intermetatarsal space to
join the first deep plantar metatarsal artery; a
branch that supplies adjacent sides of the first and
second digits; and a branch that supplies the out-
side of the first digit with one twig, and sends
another around the first metatarsal to the deep
plantar arch, and gives off an anastomotic twig to
the medial tarsal artery.
(4) A. arcuata (fig. 139) is the dorsal terminal
branch of the dorsalis pedis. It arches laterad from
the second interosseous space, forming the deep
dorsal arch by anastomosing with a descending
branch from the lateral tarsal artery. Aa. meta-
tarseae dorsales profundae 2-5 are radiated
from this arch. Each receives its corresponding
superficial dorsal metatarsal near the middle of
M. rectus femoris
M. vafitus taterali
.U. vastus mediatis
Lig. coll. fib
R. articularis.
M. ext. dig. long. (cut).
M. peromeus longus (cut)
Aa. tibiales recurrentes
N. peronaeus superf
X. peronaeus prof. - _,^,
M. peronaeus tertius
M. solew
R. nutritia fib.
A. peronaea
R. superficialis
M. peronaeus brei'is-
Rr. nutritia fib.
A. sural is
A. malleolaris ant. iat.
Rete malleolare Iat,
A. tarsea Iat.
R. nutritius tarsi
A. suralis.
R. anast. w. r. superficialis (A. tib. ant.)
Reto dorsale pedis.
A. arcuata
Aa. metatarseae plantares prof. I V
Aa. metatarseae dorsales prof. II-V
M. sartor itis (cut)
M. ext. hallucis longus
R. pcrforans
A. malleolaris ant. med.
Rr. nutritia tib.
Rete malleolare med.
A. tarsea med.
R. anast. w. r. plant, prof., A, tib. post.
A. dorsalis pedis
A. metatarseae dorsales prof. I
R. perforans
R. plantaris prof,
cus plantaris prof.
Aa. metatarseae dorsales superf.
"\^Rr. perforantes, to Aa. met. plant, sup.
Aa. digitales propreae
Aa. digitales communes
Fig. 139. Arteries and nerves of lower hind leg of Ailuropoda, anterior view.
273
274
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
the metatarsus, and the anterior perforating branch
from the plantar metatarsal at the metatarso-
phalangeal articulation. The resulting dorsal digi-
tals divide immediately into digitales propriae.
(5) R. plantaris profundus (fig. 139) is the
plantar terminal branch of the dorsalis pedis. It
perforates the second intermetatai-sal space to reach
the planta, where it joins a branch of the lateral
tarsal artery to form the deep plantar arch. This,
the Arcus plantaris profundus (fig. 139), arches
across the bases of the metatarsals, radiating the
deep plantar metatarsal arteries. Each A. meta-
tarsea plantaris profundus receives its corre-
sponding superficial plantar metatarsal near the
head of the metatarsal bone, and each resulting
common vessel gives off an anterior perforating
branch at the metatarso-phalangeal articulation,
beyond which it continues distad as the plantar
digital artery. The anterior perforating branches
join the dorsal digital arteries at the metatarso-
phalangeal articulations.
Posterior Tibial Artery
A. tibialis posterior (fig. 140), the smaller of
the two tibial arteries, accompanies the tibial nerve
superficial to the popliteal muscle. At the lower-
most quarter of the leg it divides into superficial
and deep plantar branches. The superficial plantar
branch forms the superficial plantar arch, while
the deep plantar branch terminates in the tarsus.
The posterior tibial gives rise to the following
branches:
(1) A. genu superior medialis (fig. 140) runs
medially just above the medial head of the gastro-
cnemius and beneath the femoral head of the semi-
membranosus. It emerges on the medial side of
the thigh between the femoral head of the semi-
membranosus and the adductor longus, and anas-
tomoses with the articular branch of the genu
suprema and with the doi-sal branch of the saphena.
(2) A. genu inferior medialis (fig. 140) runs
medially beneath the medial head of the gastro-
cnemius and between the two heads of the semi-
membranosus. On the medial side of the knee it
anastomoses with the superior medial genicular
and the dorsal branch of the saphena.
(3) A. genu media (fig. 140) arises from the
posterior tibial beside the origin of the superior
medial genicular. It passes directly into the knee
joint.
(4) A. suralis (fig. 140) is the largest branch
given off by the posterior tibial in the popliteal
space. It runs distad over the gastrocnemius and
plantar muscles, in which it exhausts itself. A
slender cutaneous branch runs subfascially with
N. cutaneus surae medialis, perforating the fascia
at the distal border of the biceps, where it receives
the descending branch of the large muscular ramus
of the anterior tibial. The sural terminates by
anastomosing with the much larger perforating
branch of the anterior tibial at the distal end of
the fibula.
(5) Rr. musculares arise from the posterior
tibial in its course along the leg, and pass to the
muscles of this region. The largest of these are
two vessels arising opposite one another at the
lower border of the popliteal muscle. The medial
of these two branches follows the lower border of
M. popliteus, giving off twigs to that muscle, the
flexor digitorum longus, and the posterior tibial.
It terminates at the distal quarter of the tibia as
a tibial nutrient branch. The lateral of the mus-
cular branches passes into the soleus, where it
ramifies.
(6) R. plantaris superficialis (fig. 140), the
larger of the two terminal branches of the posterior
tibial, receives the plantar branch of the saphena
near its origin, and then continues across the sole
with the medial plantar branch of the tibial nerve,
to terminate as the superficial plantar ai-ch. The
first of the superficial plantar metatarsals arising
from this arch supplies the outer side of digit 1,
and the remaining four anastomose with the corre-
sponding deep plantar metatarsals at the meta-
tarso-phalangeal joints.
(7) R. plantaris profundus (fig. 140) gives off
a slender anastomotic branch at the tibio-tarsal
articulation that passes around the medial border
of the ankle to anastomose with the descending
branch of the medial tarsal artery. The plantaris
profundus itself terminates as a nutrient artery of
the ankle joint.
Interosseous Artery
A. interossea, the third primary branch of the
popliteal artery, is gi'eatly modified and represented
only in part in Ailuropoda (fig. 142). The most
proximal part of this vessel, which typically arises
from the popliteal and runs distally through the
popliteal space, is missing. The middle section is
represented by the peroneal artery, which here is
a branch of the anterior tibial that anastomoses
distally with the perforating branch of the ante-
rior tibial. The perforating section of the interos-
seous is represented by the perforating branch of
the anterior tibial, and the distal section, which
typically continues into the dorsal pedal artery, is
represented by the distal part of the anterior tibial.
Discussion of Arteries
During ontogenetic development the anlagen of
the systemic vessels first appear as elaborate capil-
A/, adductor magnus
A. poplitea
A. genu sup<>rii)r nil.
,, , A. genu med
jVf. gastrocnemius caput medial, i{cul),
A. genu inf. med
M. semimembranosus {cut)
N. to mm. popliteus &
flexor digitorum longl
M. fiei. dig. lougus.
Arcus planLaris superf.
M. castas taleralis
A. genu sup lat.
Kr. mm. biceps fem. & tenuiasimui
N'. tibialis
'A. genu inf. lat.
,A. tibialis ant.
N'. cutan. surae med.
.V. liuralis (cut)
,U. gaslrociiemiu.1 icapnl lalrrale) {cut)
\t. solfits fcut)
\. tibialis post.
N". intensseus cruris
M. peroiiaeus tcrtius
V. ftejc. httllucis loiigus
A. suralis
Rr. nutritia tib.
R. plantaris, A. saplicna
R. plant, prof., A. tib. post.^^'
R. plant, sup., A. tib. post.C]^
N'. plantaris med
R. anast. w. A tarsea med.
.U. peroiiaeus hrecis
peronaea
N". plantaris lat.
R. nutritia fib.
R. perforans A. tibialis ant.
Tul)er calcaiiei
Teiido m. peroiiaeus toiig.
A/xmeurosis plantaris {nil)
r^a ,M. abd. <iiji. quinti
M . flex. dig. hrecis
R. anast. w. A. tarsea lat.
Fig. 140. Arteries and nerves of lower hind leg of Ailnropoda, posterior view.
275
276
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
lary netwoi-ks, the patterns formed by these net-
works becoming increasingly irregular away from
the heart. The arteries and veins arise by enlarge-
ment and differentiation of pathways through the
networks i^Copenhaver, 1955). The only function
of the vessels is to transport fluids to and from the
tissues, and obviously this can be accomplished via
an almost infinite variety of potential vessel pat-
terns. Individual variations in patterns occur, but
the choice among the multiple potential pathways
through the primary netwoi-k is not random; the
vessels form definite patterns that are faithfully
replicated in individual after individual. Definite
vessel patterns also tend strongly to be character-
istic for taxa of mammals. Several factors are
known to contribute to determining the particular
pathways that are followed, but the relative roles
of these factors are poorly understood. Experi-
mental studies (e.g., Clark, 1918, Am. Jour. Anat.,
23, p. 37; Clark et al., 1931, Anat. Rec, 50, p. 129),
and comparative studies of adult vessel patterns,
both show that heredity somehow plays an impor-
tant part, although it is not clear to what extent
vessel patterns reflect genetic factors acting directly
on the forming vessels (intrinsic factors) and to
what extent genetic factors acting on surrounding
tissues (extrinsic factors) are involved. The studies
of Sawin and Nace (1948) and Sawin and Edmonds
(1949) indicate that extrinsic factors (genetic fac-
tors at second hand, so to speak) are almost wholly
responsible. Chemical and mechanical factors as-
sociated with blood flow also play a part after
circulation is established (Copenhaver, 1955).
Comparative studies show that basic patterns
can be identified throughout the systemic circula-
tion in the Carnivora (Davis, 1941; Story, 1951),
and somewhat more broadly throughout the Mam-
malia (Tandler, 1899; Zuckerkandl, 1907; Hafferl,
1933). Variations in a particular basic pattern
occur in several different ways: (1) the site at
which a vessel ai'ises from a parent trunk may shift
proximally or distally; (2) the relative calibers of
collateral vessels or vessel systems may vary re-
ciprocally; (3) embryonic trunks may drop out in
whole or in part, their terminal ramifications hav-
ing been captured by another vessel; and (4) the
calibers of vessels vary with the physiological de-
mands of the tissues they supply.
Within the Carnivora, at least, the basic pat-
terns vary in characteristic ways among the sev-
eral families, subfamilies, and genera. Patterns
that are "primitive" in the sense that they resem-
ble those found in the most primitive placentals
tend to occur in those carnivores that display gen-
erally pi-imitive morphological features. Special-
ized vessel patterns are found in more advanced
carnivores. A hierarchy of patterns, increasingly
refined from ordinal down to generic level, is evi-
dent in all parts of the carnivore arterial system
wherever adequate samples have been studied.
Thus the arteries appear to supply trustworthy
data, which may be used to support data from
other sources, on inter-relationships among the
Carnivora.
On the other hand, the circulatory system is per-
haps unique among the organ systems in being a
passive distribution system. We can scarcely imag-
ine vessel pattern as a factor limiting adaptive
radiation within the Mammalia, nor can we visu-
alize natural selection acting directly on blood
vessels as it does on bones, muscles, nerve tissue,
etc. Thus vessel patterns are of no help in under-
standing the evolution of functional mechanisms.
At best they may reflect function; they can scarcely
direct or channel function. Within the Mammalia
the circulatory system is useful to the comparative
anatomist only as one of several sources of data
from which relationships may be inferred.
I have not tried to compare in detail all parts of
the circulatory system of Ailuropoda with other
carnivores. In general, only those parts for which
comparative data already exist will be considered.
Branches of Aortic Arch
The manner in which the carotids and subcla-
vians arise from the arch in mammals may be
gi'ouped into five types (Hafferl, 1933). All terres-
trial carnivores fall into his type II, in which both
common carotids and the right subclavian arise
from a common trunk, the left subclavian arising
independently. Parsons (1902) found that two fur-
ther subtypes of branching are represented among
terrestrial carnivores: type A, in which the two
carotids arise from the innominate independently,
and type B, in which there is a short common caro-
tid trunk after the right subclavian is given off.
Raven (1936) added several observations to those
tabulated by Parsons. I have added 11 observa-
tions on arctoids, making a total of 33 individual
arctoid carnivores for which data are available
(Table 24).
All of the 14 canids so far examined represent
type A. The Procyonidae and Ursidae are more
variable but are predominantly type B, except
Procyon lolor, which appears to favor type A. Of
the two specimens of Ailuropoda that have been
checked, one represents type A and the other
type B.
It has been commonly assumed that the type of
arch pattern in mammals depends on mechanical
factors, such as are reflected in body build, rather
than genetic factors. This opinion was confirmed
DAVIS: THE GIANT PANDA
277
by Sawin and Edmonds (1949), who concluded from
extensive breeding experiments on rabbits that
there is "little indication of dominance and segre-
gation characteristic of mendeiian inheritance,"
and that variations in the aortic arch pattern are
determined by hereditary differences in regional
growth centers in which the vessels are located.
Table 24. BRANCHES OF AORTIC ARCH IN
ARCTOID CARNIVORES
Type A Type B
Cants familiaris 4/4
Canis lupus 3/3
Cants latrans 1/1
Lycaon pictus 2/2
Vulpes fulva 1/1
Vulpes vulpes 3/3
Procyon lotor 3/4 1/4
Nasua sp 1/3 2/3
Polos flavus 1/1
Ailurus fidgens 1/1
Ailuropoda melanoleuca 1/2 1/2
Helarctos malayanus 1/1
Ursus americanus 3/3
Ursus gyas 1/4 3/4
Carotid Circulation
The pattern of the carotid circulation in the
Garni vora has been reviewed by Tandler (1899),
Davis and Story (1943), and Story (1951). Tand-
ler showed that any pattern of carotid circulation
found among mammals can easily be derived from
a single basic type (fig. 141, A). In this basic pat-
tern the common carotid terminates in three main
trunks, which apparently are always laid down
during ontogeny: the external carotid, which pri-
marily supplies extra-cranial structures except the
upper jaw and primary sense organs; the internal
carotid, which supplies the brain, eyeball, and ear;
and the stapedial, which is the primary vessel for
the upper jaw, the adnexa of the eye, and the nose.
These three trunks are interconnected by anasto-
motic vessels, through which one trunk can cap-
ture the terminal branches of another. The proxi-
mal part of a trunk disappears after its terminal
part has been captured. The carotid pattern of
any mammal can easily be derived by dropping out
sections of this basic pattern.
In adult Garnivora the stapedial artery has dis-
appeared, its terminal branches having been taken
over by the external carotid (fig. 141, B). In the
Aeluroidea the external carotid tends to take over
the internal carotid circulation as well; in the do-
mestic cat the internal carotid is completely sup-
pressed, and of the three primary trunks only the
external carotid remains. Among the Arctoidea
there are minor variations of the basic arctoid pat-
tern (Story, 1951), but these are almost wholly
associated with differences in head proportions,
muscular development, and sense organs. In gen-
eral, Ailuropoda shares more characters with the
Ursidae than with the Procyonidae or Ganidae
(Story, 1951).
A striking example of the close agreement be-
tween Ailuropoda and the Ursidae is the elongation
and looped arrangement of the subdural part of
the internal carotid. In all other carnivores the
carotid passes straight through the sinus caverno-
sus, but in a specimen of Thalarctos described by
Tandler the vessel immediately arched caudad in
the sinus, forming a long U-shaped loop twisted
around its own long axis, along the medial border
of the petrosal. I found an identical situation in
a specimen of Ursus americanus, in which the sub-
dural part of the carotid measured 60 mm. while
the linear distance traversed by this part of the
vessel was only 12 mm., a ratio of 1 : 5. Exactly
the same condition was present in Ailuropoda
(p. 252), except that the posterior prolongation
was not as extensive, with a ratio of only 1 : 3.
Branches of the Abdominal Aorta
This part of the circulatory system has received
little detailed comparative study, probably be-
cause few significant variations have been found
among mammals (Hafferl, 1933). In the dog and
cat there are no common iliacs; there is a common
hypogastric trunk, but it is very short. The pat-
tern in Ailuropoda differs little from that in the
domestic dog and cat, and resembles even more
closely the pattern in a specimen of Ursus ameri-
canus dissected by me. The only notable differ-
ence between Ailuropoda and other carnivores is
that the iliolumbalis arises from the external iliac
trunk instead of from the hypogastric trunk. This
general agreement is somewhat unexpected in view
of the shortening of the lumbar region and indica-
tions of other profound disturbances in the poste-
rior part of the axial skeleton in Ailuropoda. Sawin
and Nace (1948) concluded that variations in the
posterior aortic region in inbred races of rabbits
resulted from the interaction of regional growth
centers, which were genetically different in each
race. In other words, as in the branches of the
aortic arch, variations were determined by extrin-
sic factors.
Arteries of the Fore Limb
These vessels have been reviewed most recently
by Zuckerkandl (1907) and Hafferl (1933) for mam-
mals in general, and by Davis (1941) for the Garni-
278
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
R. anastomoticus
A. comm. post.
/ R. circ. Willisi
A. stapedia r. sup.
A. ophthalmica
A. carotis int.
A. ethmoid, ext.
^ A. ciliaris
A. stapedia
k. infraorbitalis
A. carotis ext
emp. superf
.V. mandibularis
.4. 'stapedia r. inf.
. maxillaris int.
R. anastomoticus
A. stapedia r.
A. stapedia r. inf.
Fig. 141. Basic pattern of the carotid circulation in mammals (A), and in arctoid carnivores (B). Embrj'onic vessels
that have disappeared are indicated by broken lines. Note particularly the anastomotic ramus, through which the external
carotid captures the internal carotid circulation in cats.
vora. The primary artery of the forearm, both
phylogenetically and ontogenetically, is the interos-
sea, which primitively is the direct continuation of
the brachial artery. Two collateral deep vessels,
the median and ulnar arteries, provide alternative
pathways. Three types, based on which of these
vessels is dominant, may be recognized : the interos-
sea type, the mediana type, and the ulnaris type.
Most arctoid carnivores belong to the mediana
type, although in some (Canidae, Procyon, Ailii-
rus) the median and interosseous arteries are sub-
equal in caliber.
The pattern of the arteries of the fore limb is
generally primitive in the Carnivora, and distinc-
tive patterns tend to be associated with the various
taxa. Among the arctoid carnivores the pattern
in the Canidae is very primitive and uniform with-
in the family. The Procyonidae and Ursidae (in-
cluding Ailuropoda) have a common pattern, which
is more specialized than in any other gi"Oup of car-
nivores; Procyon is somewhat aben-ant. These
arctoids are unique in that the brachial artery does
not pass through the entepicondylar foramen (al-
though the median nerve does). The bifurcation
of the common median artery into subequal me-
diana propria and medianoradial arteries tends to
be shifted distally toward the carpus; in the bears
and panda it is near the carpus. The Procyonidae
and Ursidae also share other less conspicuous fea-
tures in the arterial pattern of the fore limb. The
bears and panda agree with each other particularly
closely.
Arteries of the Hind Limb
Comparative studies of these vessels in the Mam-
malia were made by Bluntschli (1906) and Zucker-
DAVIS: THE GIANT PANDA
279
A. poplitea
A. saphena
R. plantaris
A. tibialis post.
A.perone^
R. perforans
R.^orsalis
A. tibialis ant.
R. superf.
Arcus plantaris superf.
Arcus plantaris prof.
Arcus dors, superf.
Arcus dors. prof.
Fig. 142. Diagram of chief arteries of the hind leg in the Carnivora. The remains of the primitive interossea is repre-
sented by the peroneal, the perforating branch of the anterior tibial, and that part of the anterior tibial distal to the perfor-
ating branch.
kandl (1907). Our knowledge of the patterns in
the Carnivora is much less satisfactory than for the
fore limb, although Zuckerkandl's material included
18 carnivores, and valid generalizations as to pat-
terns within the order are not yet possible.
In the thigh region the deep femoral is often ab-
sent in bears. Zuckerkandl refers specifically to
its absence in one (Helarctos) of three bears dis-
sected by him; in the second case (Melursus) he
describes a profunda, but in the third (Thalardos)
he does not state whether the profunda was pres-
ent or absent. It was absent in a specimen of
Ursus americanus dissected by me. It was also
absent in one specimen each of Procyon, Mustela,
Viverra, and Lutra dissected by Zuckerkandl. Ab-
sence of the profunda is otherwise unknown as a
normal condition in placental mammals.
The primary vessel of the lower leg and foot is
the interossea, which is laid down in the embryos
of all mammals that have been studied (Bluntschli,
1906). Three collateral vessels that develop later
the saphena, tibialis anterior, and tibialis pos-
terior provide alternative pathways to the lower
leg and foot. Each of these four vessels may be
enlarged or reduced to produce a variety of pat-
terns. Bluntschli called three of these the inter-
ossea type, the saphena type, and the [anterior]
tibial type. The fourth could be called the poste-
rior tibial type. In all Carnivora so far examined,
the anterior tibial is the main trunk of the lower
leg and foot (fig. 142). The saphena and posterior
tibial persist as relatively minor vessels, and the
interossea is partly suppressed, partly represented
by the threadlike peroneal, and distally has been
captured by the anterior tibial.
In my specimen of Ursus americanus the sa-
phena was nearly as large as the anterior tibial,
making this specimen intermediate between the
saphena and anterior tibial types.
The arteries of the hind limb in Ailuropoda do
not differ in any important respect from the carni-
vore pattern as now known.
Conclusions
1. Arterial patterns are elements of a passive
distribution system, and therefore reflect function
280
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
rather than directing function. Vessel pattern can-
not be a factor that limits or channels adaptive
radiation, and therefore is not directly subject to
natural selection.
2. \'essel patterns are not themselves inherited.
Differences are apparently produced almost exclu-
sively by differences in mechanical forces in the
vessel environment during ontogeny, and these are
hereditary. Therefore vessel patterns have a cer-
tain taxonomic value.
3. Vessel patterns characteristic of taxa are
evident throughout the arterial system in the Car-
nivora.
4. Where comparative data are available, arte-
rial patterns in Ailiiropoda resemble those of the
Ursidae more closely than those of any other fam-
ily or genus of Carnivora.
in. VEINS
Vena Cava Anterior and Its Tributaries
The anterior vena cava has an external diameter
of 20 mm., and a length of 90 mm. before it bifur-
cates to form the innominates. It receives the
following tributaries: (1) the azygos; (2) the inter-
nal mammaries; (3) the costocervical axis; and (4)
the innominates.
1. V. azygos enters the dorsal side of the vena
cava at a point about midway between the right
aiu-icle and the junction of the innominate veins,
i.e., at the level of the fifth thoracic vertebra. At
its origin the azygos lies well to the right of the
midline, but it gi-adually moves mesad until at
the level of the ninth thoracic vertebra it lies along
the midline. Immediately after its origin it gives
off a branch from its left wall that runs cephalad
to the second and third intercostal spaces. Bi-
lateral branches begin at the level of the sixth
vertebra, a large left branch supplying the fourth
right intercostal space and the third, fourth, and
fifth left intercostal spaces; the con-esponding right
branch supplies the sixth right intercostal space.
Successive intercostal branches are more or less
symmetrically arranged back to the diaphragm,
where the azygos terminates by bifurcating into
branches that supply the fourteenth intercostal
spaces.
2. Vv. mammariae internae enter the ventral
wall of the vena cava independenth^ just caudad
of the origin of the innominates. The right inter-
nal mammary enters about 15 mm. directly behind
the left. Extending obliquely ventrad, caudad,
and mesad, each joins the artery of the same name
and passes with it beneath the transverse thoracic
muscle, where it supplies the ventral intercostal
spaces.
3. Truncus costocervicalis enters the right
dorsolateral wall of the anterior vena cava at about
the same level as the right internal mammary vein.
The costocei-vical trunk runs craniad and slightly
laterad, dividing to form three branches: ( 1) V. in-
tercostalis I arises opposite the first intercostal
space, which it supplies; (2) V. vertebralis and (3)
V. cervicalis profunda arise opposite the first rib
by bifurcation of the trvmk. The vertebral vein
joins the artery of the same name, and together
they pass into the transverse foramen of the sixth
cervical vertebra. The deep cervical vein slightly
exceeds the vertebral vein in caliber. It runs cra-
niad with the deep cervical artery.
4. Vv. anonymae arise by bifurcation of the
anterior vena cava at the level of the posterior bor-
der of the firet rib. Each innominate is very short,
breaking up to form the axillary and jugulars im-
mediately in front of the rib. V. jugularis ante-
rior is an unpaired vessel arising from the medial
wall of the left innominate, about midway in the
course of the latter. Running craniad along the
ventral midline of the trachea, the anterior jugular
gives off the V. thyreoidea posterior at the level
of the hyoid. Here it bifurcates, each branch run-
ning laterad and craniad to anastomose with the
lingual vein.
Internal Jugular Vein
V. jugularis interna arises from the medial
wall of the innominate, thus from the convex side
of the curve of the latter vein as it arches around
the first rib. The left internal jugular arises some-
what farther distad than the right, probably be-
cause of the origin of the anterior jugular from the
left innominate. Each internal jugular nins cran-
iad beside the corresponding common carotid ar-
tery, the vein lying toward the outside. The
diameter of the internal jugular is 4 mm. V. thy-
reoidea anterior dextra arises at the level of the
artery of the same name. A smaller branch open-
ing independently into the internal jugular immed-
iately caudad of the anterior thjToid apparently
corresponds to the occasional V. thyreoidea me-
dia of human anatomy. V. thyreoidea anterior
sinistra opens into the left jugular 25 mm.caudad
of the corresponding arteiy.
At the level of the cricoid cartilage the inter-
nal jugular receives the large R. anastomotica,
which lies mesad of the vagus nerve. The anasto-
motic branch gives off two large vessels to the ver-
tebral vein, as well as smaller twigs to the pha-
ryngeal plexus. Much diminished in caliber, the
anastomotic ramus enters the foramen lacenun
posterior where it empties into the inferior petro-
sal sinus.
DAVIS: THE GIANT PANDA
281
The internal jugular accompanies the carotid ar-
tery as far craniad as the origin of the digastric
muscle, where the vein and artery diverge. As the
vein approaches this point it crosses over the ar-
tery, passing ventrad of it. The internal jugular
continues anteriorly beside the glossopharyngeal
nerve to the base of the postglenoid process, where
it receives numerous pharyngeal branches from the
pharyngeal plexus and terminates by uniting with
the medial branch of the internal facial vein. The
pharyngeal plexus is a network of veins draining
the walls of the pharynx, from the level of the fora-
men magnum to the posterior nares. One of the
pharyngeal rami communicates with the sinus cav-
ernosus through the foramen lacerum medium.
Venous Sinuses of the Dura Mater
The combined veins of the vertebral canal pass
through the foramen magnum into a deep exoccip-
ital groove that opens at the hypoglossal canal into
the sigmoid groove for the transverse sinus. The
sinus transversus extends from the opening of the
superior petrosal sinus, laterally, to the posterior
lacerated foramen, medially. The sinus petrosus
superior is entirely surrounded by bone, beginning
at the posterosuperior angle of the petrosal bone
and running along its superolateral margin. The
superior petrosal sinus is large posteriorly, where
it drains into the lateral branch of the internal
branch of the internal facial vein through the post-
glenoid foramen. Anterior to this foramen the
superior petrosal sinus is a narrow canal opening
from the sinus cavernosus at the lateral wall of
the foramen ovale. The sinus petrosus inferior
is the direct continuation of the transverse sinus
from the foramen lacerum posterior to the dor-
sum sellae, where it becomes the cavernous sinus.
The sinus cavernosus fills the sella turcica and
opens anteriorly into the ophthalmic vein.
External Jugular Vein
V. jugularis externa (figs. 107, 131), with a
diameter of 9 mm., is considerably larger than the
internal jugular. The external jugular enters the
innominate vein between the internal jugular and
axillary veins, and runs forward immediately lat-
erad of the sternomastoid muscle, dividing at the
posterior border of the submaxillary gland to form
the external and internal facial veins. Only one
branch, the thyrocervical trunk,' is received in the
cervical region.
' This designation is used for this trunk because the
branches that it receives are practically identical with
the branches of the thyrocervical artery. This condition
is quite different from the usual arrangement in man, the
domestic cat, etc.
The transverse scapular arises from the jugular on the
right side of the body (cf. p. 283), but this does not seem to
be the normal condition.
V. thyreocervicalis is a large vessel entering
the external wall of the external jugular about
50 mm. craniad of the origin of the latter. It
curves away from the jugular to join the thyro-
cervical artery, which it accompanies toward the
scapulo-humeral articulation. The vein receives
the following tributaries: (1) The large V. trans-
versa colli enters the thyrocervical 40 mm. beyond
the origin of the latter. It joins the corresponding
artery, accompanying it around the shoulder joint
to the lateral shoulder region. About 10 mm. far-
ther distad the thyrocervical bifurcates to form
two branches of approximately equal size: (2) a
large muscular ramus that accompanies the corre-
sponding artery to the proximal part of the clavo-
trapezius and adjacent muscles, and (3) the cephalic
vein (p. 284).
Internal Facial Vein
V. facialis interna (posterior) (figs. 107, 131,
132) arches dorsad and craniad to the base of the
ear, in front of which it terminates by entering the
postglenoid foramen, to be continued within the
skull as the transverse sinus. V. sternocleido-
mastoidea arises from the internal facial near its
base; it accompanies the artery of the same name.
V. auricularis and V. occipitalis arise by a com-
mon trunk, as was the case with the correspond-
ing arteries; the ramifications of both veins agree
closely with those of the arteries, except that the
main auricular veins do not come from this trunk.
The occipital vein gives off the large Vv. mas-
toideae, which communicate with the sinus trans-
versus.
V. temporalis superficialis (fig. 132) is a pow-
erful vein given off over the base of the ear carti-
lage. It gives off a stout branch at its base that
runs across the root of the zygoma to anastomose
with the transverse facial; twigs from this branch
go to the masseter and to the postglenoid rete.
V. transversa facei arises higher. It receives the
anastomotic branch described above, then joins a
masseteric branch of the artery of the same name
and runs anteriorly with it. V. auricularis an-
terior (fig. 107), the larger of the two accompany-
ing veins of the anterior auricular artery, arises
opposite and a little above the transverse facial.
It joins the corresponding artery, and passes with
it onto the front of the ear. V. auricularis pos-
terior comes off at the upper third of the root of
the zygoma. It gives off twigs to the base of the
pinna, receives an anastomotic twig from the oc-
cipital-auricular trunk, gives off a slender accom-
panying branch of the anterior auricular artery,
and then joins the posterior auricular artery at the
level of the dorsal border of the zygoma. Its fur-
282
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
ther ramifications agree with those of the corre-
sponding artery. Beyond the origin of the posterior
auricular, the temporal trunk is continued as V.
temporalis media. The ramifications of this vein
agree with those of the artery of the same name.
Immediately beyond the origin of the superficial
temporal the internal facial vein arches sharply
mesad around the mastoid process. Twigs are
given off in this region to the parotid and submax-
illar}^ glands. In front of the mastoid process arises
the small V. stylomastoidea, which passes into
the stylomastoid foramen. Opposite this a slender
vessel arises and passes across the medial part of
the mandibular condyle, laterad of the postglenoid
process, to join the pterygoid rete farther anteri-
orly. Twigs arising from this vessel near its base
form a delicate postglenoid rete on the postglenoid
process.
The internal facial appears to bifurcate in front
of the mastoid process to form two vessels of ap-
proximately equal size. One of these, which may
be regarded as the continuation of the internal
facial trunk, soon enters the postglenoid foramen.
The postglenoid foramen leads into a bony canal
that passes dorsad in front of the auditory meatus,
to open into the cerebellar cavity of the skull. Be-
yond this canal the vein continues as the trans-
verse sinus.
The other terminal branch of the internal facial
is V. maxillaris interna (figs. 131, 132). This
vessel arches around the base of the postglenoid
process, to be joined by the terminus of the inter-
nal jugular at the medial border of that process.
The resulting common trunk passes forward be-
tween the medial border of the postglenoid process
and M. levator veli palatini, to break up into the
pterygoid plexus at the posterior border of the
temporal fossa.
The Plexus pterygoideus gives rise to the fol-
lowing branches:
1. Vv. alveolaris inferior (paired accompanying
veins).
2. V. temporalis profunda posterior.
3. V. masseterica.
4. V. tympanica anterior.
5. V. foramina ovalis (accompanies A. meningea
accessoria).
6. Vv. pterygoidei.
7. V. meningea media.
These vessels, with the exceptions noted, accom-
pany the corresponding arteries.
Anteriorly the pterygoid plexus drains into a
powerful anastomotic branch, which passes along
the ventral border of the buccinator muscle to
empty into the inferior labial vein near the juncture
of the latter with the external facial. Numerous
small Vv. buccinatoria and a large V. alveolaris
superior posterior empty into the anastomotic
branch in its course along the muscle.
External Facial Vein
V. facialis externa (anterior) (figs. 107, 131,
132) follows the anterior border of the masseter
forward and upward to a point in front of the an-
terior root of the zygoma. Continuing upward in
front of this root of the zygoma, it divides in front
of the orbit into the external nasal and nasofrontal
veins. The external facial receives the following
tributaries along its course:
1. A transverse communicating branch passes
from the external facial near the posterior end of
the digastric, to the sublingual branch of the ante-
rior jugular. A twig from this communicating
branch passes forward between the mylohyoid and
hyoglossus, to anastomose with the lingual vein.
2. V. submentalis enters the external facial
directly opposite the preceding branch. It receives
a twig from the submaxillary gland, then passes
across the digastric and between the digastric and
masseter to the superficial surface of the mylo-
hyoid. Here it joins the submental artery, and
the further course of the two vessels agrees closely.
3. V. labialis inferior (figs. 107, 131) is re-
ceived at the posterior end of the exposed part of
the inferior alveobuccal gland. The vein passes
forward with the artery on the mandible, the rami-
fications of the two vessels agi-eeing.
4. A muscular twig from the platysma enters
the external facial a few millimeters farther distad.
5. V. facialis profunda (figs. 107, 132) enters
the deep surface of the external facial at the dorsal
border of the inferior alveobuccal gland. It lies
directly beneath the external facial as far as the
lower border of the zygoma, then passes behind the
anterior root of the zygoma to the common outlet
of the sphenopalatine foramen and pterygopala-
tine canal. Just before reaching the foramina the
trunk divides into a V. sphenopalatina and a
pair of small Vv. palatina descendens. These
vessels enter the foramina with the corresponding
arteries.
V. alveolaris superior anterior enters the deep
facial at its base, and numerous smaller alveolar
twigs from the minute foramina below the orbit
open into the deep facial along its course. There
are also muscle twigs from the temporal muscle.
Below the orbit the deep facial gives off a large
communicating branch, which pierces the ventral
wall of the periorbita to anastomose with the infe-
DAVIS: THE GIANT PANDA
283
rior ophthalmic; a twig from this branch passes
out of the ventral side of the orbit, to anastomose
with the angular vein on the face.
Just beyond the deep facial, the external facial
receives a common trunk formed by (6) a muscular
branch from the masseter and (7) V. labia lis supe-
rior (fig. 107).
8. A communicating branch arising in front of
the anterior root of the zygoma arches upward and
backward across the temporal muscle, to anasto-
mose with the anterior auricular vein.
9. V. angularis (fig. 107), which enters the ex-
ternal facial just above the foregoing, follows the
angular artery.
10. Several nutrient twigs from the jugal enter
below and in front of the orbit.
11. V. nasofrontalis (fig. 107), the more pos-
terior of the two terminal vessels, arches around to
the dorsal side of the orbit. Just above the orbit
it receives V. frontalis, which follows the corre-
sponding artery. The nasofrontal then anasto-
moses with the superior ophthalmic vein, which it
meets immediately above the eye but outside the
periorbita.
12. V. nasalis externa (fig. 107), the anterior
of the terminal vessels, passes forward on the side
of the nose. Several communicating branches pass
up over the bridge of the nose, to anastomose with
corresponding vessels from the opposite side. At
the nasal aperture the trunk of the external nasal
vein bifurcates, a dorsal and a ventral branch anas-
tomosing with corresponding vessels from the oppo-
site side to encircle the nasal cartilages immediately
in front of the premaxillary and nasal bones.
Ophthalmic Vein
V. ophthalmica arises from the sinus caverno-
sus, from which it passes into the orbit through
the orbital fissure. The vessel runs forward in the
orbit, to be perforated by the orbital artery at
about the posterior third of the orbit. At this
point the ophthalmic breaks up into its terminal
branches.
1. V. ophthalmica superior, by far the larg-
est of the terminal branches, accompanies the fron-
tal artery through the dorsal wall of the periorbita.
V. ethmoidalis, which accompanies the corre-
sponding artery through the ethmoidal foramen,
enters the vessel near the posterior end of the orbit.
As it passes anteriorly the superior ophthalmic re-
ceives a muscle twig that perforates the periorbita
independently. Directly above the eye, and just
before passing out of the orbit, it receives a vein
that emerges from the frontal sinus through a
small foramen in the dorsomedial wall of the or-
bit. Upon emerging from the orbit the superior
ophthalmic becomes the nasofrontal vein, and
this communicates openly with the external facial
vein.
2. V. centralis retinae is a thread-like vessel
that comes off immediately below the superior oph-
thalmic. It joins the deep branch of the orbital
artery and follows it (and the central retinal artery
in which the orbital artery terminates) into the
optic nerve and thence into the eye ball.
3. V. lacrimalis follows the corresponding ar-
tery to the lacrimal gland, where it anastomoses
with a twig from the angular vein.
4. Vv. musculares, two in number, supply the
ocular muscles.
5. V. ophthalmica inferior, the most ventral
branch of the ophthalmic, runs toward the eye
between M. rectus inferior and the periorbita. It
terminates by anastomosing with the communi-
cating branch of the deep facial vein immediately
below the eye.
Axillary Vein
V. axillaria is the largest and most posterior of
the triad of branches in which the innominate ter-
minates.' The left axillary (14 mm. in diameter)
is considerably larger than the right (11 mm.).
The axillary arches around the anterior border of
the first rib, becoming the brachial vein beyond the
point where it receives the subscapular trunk. It
has a length of about 70 mm. The axillary receives
the following tributaries: (1) A small branch enters
the anterior wall of the axillary 20 mm. beyond the
origin of the external jugular. It bi'eaks up into a
number of branches that drain the longus colli and
the anterior end of the scalenus; the largest branch
passes ectad beside the axillary artery, to anasto-
mose with a branch from the internal circumflex
humeral. (2) V. thoracoacromialis enters im-
mediately distad of the preceding vein. It accom-
panies the corresponding artery. (3) A muscular
ramus, nearly as large as the thoracoacromialis
and entering immediately behind and ventrad of
it, drains the anterior parts of the superficial and
deep pectoral muscles. (4) V. transversa scap-
ulae on the right side of the body enters the exter-
nal wall of the external jugular 45 mm. beyond the
origin of the latter. On the left side it empties into
the axillary a few mm. distad of the thoracoacrom-
ialis. The vein accompanies the corresponding
artery into the space between M. suprascapularis
and M. infraspinatus; its branches correspond
' The arrangement of the vessels in this region, particu-
larly the origin of the transverse cervical and transverse
scapular veins from the external jugular, makes it impos-
sible to distinguish a deflnitive subclavian vein.
284
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
closely with those of the artery. (5) V. thora-
calis anterior enters the posterior wall of the
axillary slightly distad of the preceding branches.
It accompanies the corresponding artery. (6) V.
thoracalis lateralis enters the posterior wall of
the axillary immediately before the latter divides
to form the subscapular and brachial veins. It
accompanies the corresponding artery to the deep
pectoral and panniculus muscles, but does not re-
ceive the intercostal branches. About 70 mm. be-
yond its origin the axillary vein of the left fore leg
bifurcates to form two branches of nearly equal
size: (7) V. subscapularis, into which both cir-
cumflex humerals empty, and (8) V. brachialis.
On the right leg the subscapular enters the axillary
at the same level as it does on the left leg, but does
not receive the circumflex humerals and conse-
quently is much smaller. The circumflex humerals
of this leg empty into a common trunk 20 mm. in
length, which enters the axillary independently
immediately distad of the subscapular.
The subscapular vein accompanies the subscap-
ular artery, receiving branches that with a few
exceptions conform closely to the branches of the
artery. The large arterial ramus to the latissimus
and subscapular muscles is accompanied by two
veins whose ramifications do not correspond ex-
actly with those of the artery. The more proximal
of the two veins receives the intercostal branches
(which in the arterial system come from the lateral
thoracic) and the branch draining the latissimus;
the distal branch drains the subscapular, teres
major, and teres minor.
The two circumflex humerals, whose ramifications
conform closely with those of the corresponding
arteries, enter the subscapular vein independently.
V. circumflexa humeri interna is composed of
a pair of collateral vessels (a single vessel on the
right leg) that enter the anterior wall of the sub-
scapular 15 mm. beyond the origin of the latter
vein. The two collateral trunks embrace the sub-
scapular artery between them, immediately be-
yond which they are connected by a transverse
communicating anastomosis. V. circumflexa
humeri externa accompanies the corresponding
artery through the septum between the long and
lateral heads of the triceps onto the lateral side of
the shoulder. It then runs along the ventral bor-
ders of the spinodeltoid and acromiodeltoid to the
cephalic vein, into which it opens.
Brachial Vein and Its Tributaries
V. brachialis is the continuation of the axillary
beyond the origin of the subscapular trunk. It lies
mesad and slightly caudad of the corresponding
artery, to which its course and branchings conform
very closely as far as the elbow. Here, anterior to
and slightly proximad of the entepicondylar fora-
men, the brachial bifurcates to form two vessels of
approximately equal size: the superficial brachial
and a trunk from which the ulnar and interosseous
veins arise. This trunk receives Vv. collateralis
radialis, recurrens radialis, and recurrens ul-
naris before its bifurcation.
V. brachialis superficialis accompanies its ar-
tery distad on the forearm, receiving a large com-
municating branch from the cephalic in the lower
third of the forearm, to the radiocarpal articula-
tion. Here it divides into volai- and dorsal branches.
The volar branch forms an arch with the ulnar vein
which conforms closely to the superficial arterial
arch. The dorsal branch passes around the base
of the radial sesamoid onto the dorsum, where it
forms an anastomotic arch with the cephalic; the
digital veins from digits 1, 2, and 3 open into this
arch, and a perforating branch pierces the inter-
stitium between the second and third metacarpals
to form the deep volar arch with a branch from
the ulnar.
Vv. ulnaris, interosseus dorsalis, and inter-
osseus volaris arise together at the level of the
corresponding arteries, accompanying them distad
and conforming closely to their ramifications.
Cephalic Vein
V. cephalica (fig. 134) arises as one of the ter-
minal branches of the thyrocervical vein. Passing
around in front of the head of the humerus, be-
neath M. clavotrapezius, it emerges on the lateral
side of the shoulder. Here it receives the external
circumflex humeral, and then runs distad over the
biceps and brachioradialis to the hollow of the
elbow. Joining the lateral ramus of the superficial
branch of the radial nerve on the flexor side of the
forearm, it runs distad with it to the carpus. Here
it divides into radial and ulnar branches. The
radial branch forms an arch with the anterior bra-
chial on the radial side of the dorsum, while the
ulnar branch forms a similar arch with a branch of
the ulnar vein on the ulnar side of the dorsum.
The dorsal digital veins open into the resulting
compound arch, the veins from the first, second,
third, and radial side of the fourth into the radial
arch, and the veins from the ulnar side of the fourth
and from the fifth digits into the ulnar arch. There
is a slender accessory vein from the ulnar side of
the fifth digit.
Vena Cava Posterior and Its Tributaries
The vena cava posterior (fig. 135) is double up
to the level of the renal veins; the undivided ante-
DAVIS: THE GIANT PANDA
285
rior part of the postcava is only 55 mm. long.' The
undivided part receives the following tributaries:
1. Vv. phrenicae posterior enter the vena
cava on either side, just anterior to the renal veins.
Thus the right is considerably farther forward than
the left. Each posterior phrenic receives a short
V. suprarenalis as it passes across the suprarenal
gland.
2. Each V. renalis enters by a short trunk
common to it and the lumboabdominal. The right
is 25 mm. farther anterior than the left. As it
approaches the kidney, the renal first receives a
branch from the posterior part of the kidney, then
two branches from the middle and anterior parts
of the kidney, respectively.
3. V. lumboabdominalis joins the renal pos-
teriorly on the right side and anteriorly on the left.
Each joins its corresponding artery, which it fol-
lows closely.
Hypogastric Veins
V. hypogastrica (fig. 135) unites with the ex-
ternal iliac to form the common iliac. The junc-
tion takes place slightly anterior to the junction
of the corresponding arteries. As usual, the vein
differs from the artery in not having separate pari-
etal and visceral divisions. The vein lies lateral
to, and between, the parietal and visceral rami of
the artery.
V. sacralis media enters the right hypogastric
immediately before the latter enters the common
iliac. From here the middle sacral runs diagonally
caudad and mesad to the midline, where it joins the
middle sacral artery and runs with it into the tail.
V. glutaea anterior, one of the two main trib-
utaries of the hypogastric, enters its medial wall
20 mm. before its termination. Beyond this point
the hypogastric continues posteriorly as a common
trunk formed by the union of the middle and pos-
terior hemorrhoidal, posterior gluteal, perineal, and
penial veins. The courses of these veins corre-
spond with those of the arteries of the same names.
' Raven found a similar condition in his specimen of Ailu-
ropoda, so a double postcava may be normal for this species.
Among the bears, the postcava divides at the normal level
in a specimen of Ursiis atnericanus figured by Raven, and
in a specimen of Ursiis americanus dissected by me. Raven
described and figured a double postcava for Ailurus fulgens;
this vessel was normal, but the precava was double in a
specimen of Ailurus described by Sonntag (1921), and the
postcava divides normally, at the same level as the abdom-
inal aorta, in a specimen of Ailurus dissected by me. Accord-
ing to Beddard (1909) a double postcava occurs frequently
in the Mustelidae. McClure and Huntington (1929) showed
that the occurrence of a double postcava in placental marn-
mals represents the persistence of parts of the embryonic
system of cardinal veins. In view of other indications of
disturbance in the lumbosacral region in Ailuropoda, the
occurrence of a double postcava is interesting.
Portal System
The portal vein arises in the porta of the liver
by the union of short right and left branches com-
ing from the liver substance. Running caudad
across the caudal lobe, it gives off (1) the splenic
vein dorsad of the cervix of the pancreas, and im-
mediately posterior to this (2) the pyloric vein.
V. coronaria ventriculi is absent, the pyloric
vein supplying the parts normally supplied by it.
A few millimeters caudad of the pyloric vein the
portal vein divides to form (3) the large anterior
mesenteric vein and (4) the smaller posterior mesen-
teric vein. The total length of the portal vein is
about 60 mm.
1. V. lienalis conforms closely to the artery of
the same name, following the curvature of the gas-
trolienal ligament and radiating branches to the
spleen which correspond to the splenic branches of
the splenic artery.
2. V. pylorica is slightly smaller than the
splenic vein, and arises from the portal vein just
caudad of it. The pyloric vein immediately curves
sharply cephalad, passes ventrad of the splenic vein,
and accompanies the right gastric artery around
the lesser curvature of the stomach. Branches are
given off to the pancreas, to the duodenum, to the
stomach along the whole lesser curvature, and to
the esophagus.
3. V. mesenterica anterior may be described
as the posterior continuation of the portal vein.
It arises near the anterior mesenteric artery, and
its course and branchings follow the arrangement
of that artery very closely. The termination of
the vein anastomoses with the termination of the
ileocolic vein in the region of the ileum.
4. V. mesenterica posterior arises from the
portal vein caudad of the origin of the pyloric vein.
It promptly breaks up into a number of veins
that supply the ileocolic region. The anterior
and middle colic veins come off by a very short
common trunk near the origin of the posterior
mesenteric; the vein then continues as the ileo-
colic vein, dividing farther distad to form two
main branches.
Vv. colica anterior and media conform closely
to the arteries of the same names. The anterior colic
vein divides into anterior and posterior branches
near the intestine. The anterior branch anasto-
moses with the posterior branch of the ileocolic,
giving off short twigs to the colon; the posterior
branch anastomoses with a small anastomotic
branch given off by the middle colic. The middle
colic supplies the entire posterior half of the
colon.
286
FIELDIAXA: ZOOLOGY MEMOIRS, VOLUME 3
Common Iliac Veins
The conunon iliac veins (V. iliaca communis,
fig. 135) run craniad as far as the middle of the
kidneys before they unite to form the posterior
vena cava. The confluence of the common iliacs
takes place slightly to the right of the midline, and
ventrad of the aorta, at the level of the first lum-
bar vertebra. The common iliacs receive the fol-
lowing tributaries: d) Vv. spermatica internae
enter symmetrically, 20 mm. anterior to the origin
of the internal spermatic arteries, at the confluence
of the common iliacs. Each accompanies its con-e-
sponding artery to the testis, with a branch coming
from the posterior renal fat. (2j Vv. lumbales
consist of two vessels entering the mediodorsal wall
of the right common iliac. The first of these is a
large vessel entering 20 mm. behind the confluence
of the two common iliacs. Branches are distrib-
uted from this trunk to the first three lumbar ver-
tebrae. The second lumbar vein enters the common
iliac at the junction of the third and fourth lumbar
vertebrae; it is distributed to the fourth and fifth
lumbars. (3) V. circumflex ilium profunda en-
ters the lateral wall of each common iliac at the
level of the coiTesponding artery. Its bi-anches are
the same as those of the artery. At the level of
the articulation between the first and second sacral
vertebrae the common iliac divides to form the
h\T)ogastric and external iliac veins.
External Iuac Vein
V. iliaca externa (fig. 135) is much the larger
of the two roots of the common iliac. Running
across the iliimi in front of the iliopectineal emi-
nence, it passes through the femoral ring posterior
to the corresponding artery, and becomes the fe-
moral vein. The external iliac receives the follow-
ing branches: ( 1) V. iliolumbalis enters the medial
wall at the level of the corresponding artery-, whose
branches it follows. (2) V. epigastrica posterior
enters its medial wall at the iliopectineal eminence,
i.e., at the level of the corresponding artery. The
course of the vein agrees closely with that of the
artery, branching to form V. spermatica externa
and the posterior epigastric proper. (3) V. pro-
funda femoris enters the external iliac at the fe-
moral ring. It joins the deep femoral artery, and
the course of the two vessels is similar. The main
trunk of the vein consists of an anastomotic branch
with the popliteal vein.
V. femoralis lies posterior to the femoral artery
in the upper part of the thigh, but just below the
middle of the thigh it becomes superficial to ime-
sad ofi the artery. It receives two branches, V.
circumflexa femoris lateralis and V. muscu-
laris posterior, which agree closely with the cor-
responding arteries. At almost exactly the middle
of the thigh the femoral vein di\'ides to form the
great saphenous and popliteal veins. The pop-
liteal considerably exceeds the great saphenous in
caliber.
V. saphena magna runs distad with the corre-
sponding artery and the saphenous ner\'e. In the
thigh its branchings correspond closely with those
of A. genu suprema, in addition to a large muscle
branch that runs forward to the knee. Between
the distal ends of the heads of the semimembrano-
sus it receives a slender branch that accompanies
the plantar branch of the saphenous arter\' to near
the distal end of the tibia, where it anastomoses
with the tibialis posterior. Just beyond the distal
end of the tibia the saphena magna receives an
anastomotic branch, chiefly from the tibialis pos-
terior, that runs around the tibial border of the
tai-sus. At the distal end of the tai-sus it receives
a smaller anastomotic branch from the tibialis an-
terior. The dorsal venous arch is formed chiefly
by the saphena magna, supplemented by two small
terminal twigs of the saphena parva and the super-
ficial branch of the anterior tibial. Five dorsal
metatarsal veins arise from the arch, and accom-
pany the corresponding arteries to the toes.
V. poplitea accompanies the popliteal artery
into the popliteal space, where it breaks up into
a number of terminal branches. As the vein enters
the popliteal space it receives a perforating branch
that corresponds to the perforating bi-anch of the
femoral artery. The popliteal vein receives the
following tributaries in the popliteal space, in addi-
tion to various muscle branches:
1. An anastomotic bi^anch with the profunda
femoris, which does not accompany an arten.',
runs proximad between the heads of the semi-
membranosus.
2. A genicular trunk is formed by veins whose
ramifications agree with those of the genicular
arteries.
3. V. saphena parva enters the posterior wall
of the popliteal at about the center of the popliteal
space. It runs distad on the back of the leg be-
neath the biceps, hing successively across the lat-
eral head of the gastrocnemius and the soleus. At
the distal end of the fibula it receives a strong anas-
tomotic branch from the tibialis posterior, then
continues along the lateral border of the tarsus
and foot.
A twig arising from the saphena parva at the
distal end of the fibula passes onto the tarsus,
where it is joined by the distal end of the super-
ficial anterior tibial vein; the resulting common
trunk joins the much larger saphena magna to
form the superficial dorsal arch. At the tarso-
DAVIS: THE GIANT PANDA
287
metatarsal articulation the saphena parva gives
off a branch that passes across the dorsum of the
foot to the space between digits 4 and 5, where it
is joined by a branch from the superficial arch to
form the digital vein to the outer side of digit 5.
The saphena parva continues along the lateral
border of the foot, anastomosing at the metatarso-
phalangeal articulation with the vein that supplies
the outer side of digit 5.
4. V. suralis enters the popliteal where that
vessel bifurcates into the anterior and posterior
tibial veins. In addition to muscle branches to
the plantaris and both heads of the gastrocnemius,
it receives an anastomotic twig arising from the
saphena parva near the distal end of the soleus.
5. V. tibialis anterior is slightly larger than
the posterior tibial vein. It accompanies the ar-
tery of the same name through the proximal end
of the interosseous space and distad along the an-
terolateral aspect of the leg, its branches cori'e-
sponding closely to those of the artery. At the
middle of the leg it divides into a larger lateral and
a smaller medial branch, which flank the artery.
V. tibialis anterior superficialis arises from
the lateral branch at the lower third of the leg and
accompanies the superficial branch of the anterior
tibial artery onto the dorsum of the foot. Here it
joins a branch from the saphena parva, the result-
ing common trunk forming one end of the super-
ficial dorsal arch.
The medial accompanying vein gives off V. tar-
sea medialis at the tibio-tarsal articulation, an
anastomotic branch to the saphena magna in the
proximal part of the tarsus, and an anastomotic
branch with the lateral accompanying vein in the
proximal metatarsal region, and terminates by
opening into the second superficial dorsal meta-
tarsal vein.
The lateral accompanying vein gives off the large
V. tarsea lateralis at the tibio-tarsal articulation.
The lateral tarsal supplies a nutrient vein to the
tarsus. At the second inter-metatarsal space the
lateral accompanying vein gives rise to two per-
forating branches that pass through to the deep
plantar arch. The deep dorsal arch is composed
of two parallel vessels that flank the corresponding
artery. The more distal of these, in which the lat-
eral accompanying vein terminates, gives off Vv.
metatarseae dorsales profundae 3 5, which en-
ter the corresponding superficial veins near the
heads of the metatarsals.
6. V. tibialis posterior accompanies the pos-
terior tibial artery along the back of the leg. Near
the distal end of the tibia it gives off a strong anas-
tomotic branch, which passes across the leg deep
to the tendon of Achilles and M. soleus, to the
saphena parva. The tibialis posterior is continued
beyond the anastomotic branch, considerably re-
duced in caliber, to the tibio-tarsal articulation.
Here it divides into a superficial branch that runs
around the medial side of the tarsus to anastomose
with the saphena magna, and a deep branch that
anastomoses with the nutrient branch of the prox-
imal part of the tarsus.
A powerful trunk arises from the transverse anas-
tomotic branch that passes between the saphena
parva and the posterior tibial. This trunk runs
distad beneath the shaft of the calcaneum, break-
ing up at the posterior border of the astragalus into
a leash of three vessels that form both plantar
arches. The medial of the three supplies the me-
dial side of digit 1. The middle one forms the arch
proper by anastomosing with a twig from the sa-
phena parva. Branches to the lateral side of digit 1,
to adjacent sides of digits 2, 3, and 4, and to the
medial side of digit 5 arise from the arch; each is
joined by the corresponding deep plantar meta-
tarsal vein. The lateral branch runs to the lateral
side of the tarsus, where it receives the terminal
branches of the lateral tarsal vein. At the middle
of the tarsus the vessel divides into medial and
lateral branches. The medial branch arches across
the sole, giving off an anastomotic branch to the
saphena magna and terminating by entering the
perforating branch of the anterior tibial. The lat-
eral branch runs down the lateral border of the
ankle, then arches across the sole to form the prox-
imal of the two deep plantar arches. It terminates
by entering the perforating branch of the anterior
tibial vein.
DUCTLESS GLANDS
I. HYPOPHYSIS
The hypophysis (fig. 144) is a flattened pear-
shaped structure situated posterior and slightly
ventral to the optic chiasma. It is connected to
the floor of the third ventricle by a short infundib-
ulum. The hypophysis lies almost horizontally in
the sella, which in Ailuropoda is deep, with promi-
nent anterior and posterior processes. The hy-
pophysis measures 10.5 mm. in length, about 9 mm.
in transverse diameter (measured after bisection),
and 5.5 mm. in vertical diameter. The organ was
not weighed.
In sagittal section the hypophysis is seen to be
composed of a smaller anterior lobe lying anteri-
orly and ventrally, and a larger neural lobe lying
posteriorly and dorsally. The pars intermedia could
not be differentiated macroscopically from the pars
posterior. A dark-colored pars tuberalis embraces
the infundibular stalk as far forward as the optic
chiasma. As in the Ursidae, a well-developed re-
cessus hypophysis extends from the bottom of the
third ventricle through the infundibular stalk and
into the posterior lobe nearly to its posterior end.
Below the recessus hypophysis a hypophyseal cleft
separates the anterior lobe from the posterior lobe,
as it does in the bears; there is no cleft above the
recessus.
In an adult female Ursus americanus the hy-
pophysis is similar in size and topography to that
of Ailuropoda but is less broadened and flattened.
In this bear it measures 12.2 mm. in length, 6.6
mm. in transverse diameter, and 6.5 mm. in ver-
tical diameter.
The hypophysis of Thalarctos and Ursus arctos
were described by Hanstrom (1947), and that of
Ailurus fulgens by Oboussier (1955). The topog-
raphy of the hypophysis in Ailuropoda closely
resembles that of the bears and lesser panda (es-
pecially the bears) and differs considerably from
that of the Canidae. Except for a very brief de-
scription of the hypophysis of Potos by Oboussier,
the structure of this organ in the Procyonidae is
unknown.
II. THYROID
The thyroid is composed of the customary pair
of lateral lobes that lie on either side of the tra-
chea, and are connected by a narrow isthmus. The
lobes are somewhat asymmetrically situated in the
specimen dissected, the left being more posterior
than the right. This condition is reflected in the
direction of the isthmus, which runs diagonally in-
stead of transversely.
Each lobe has a length of about 55 mm. and a
width of about 20 mm. The right lobe extends
from the cricoid cartilage back to the sixth tra-
cheal ring; the left from the second tracheal ring
to the tenth. The isthmus crosses the seventh
tracheal ring.
The thyroid is supplied by anterior and poste-
rior vessels, which come from the thyrocervical
trunks and the internal jugular veins.
III. PARATHYROID BODIES
The parathyroids appear as a pair of small oval
whitish structures on the dorsal surface of the thy-
roid gland. They are symmetrically placed, one
being located on each lateral lobe about 20 mm.
from its anterior tip. Each body measures about
12 mm. in length and 4 mm. in width. The left
body is partly buried in the substance of the thy-
roid, while the right lies wholly on the surface.
IV. THYMUS
The thymus is an elongate bilobed gland, pale
chocolate brown in color. It is rather well devel-
oped, with a length of 117 mm. The gland lies
wholly within the mediastinum, its anterior end
reaching only slightly beyond the middle of the
first costal cartilage. The left lobe considerably
exceeds the right in size. Both lobes lie to the left
of the left innominate vein, and are crossed ven-
trally by the left mammary artery and vein.
A quantity of fat at either end of the thymus
indicates that regression of this structure was well
under way.
The thymus is supplied by branches from the
mammary vessels.
288
NERVOUS SYSTEM
I. BRAIN
The brain of the adult female giant panda Pan
Dee was described briefly by Mettler and Goss
(1946). The description given here is based on
the brain of the subadult male Su Lin. It was
embalmed in situ and later removed by sectioning
the skull. The brain was undamaged.
The brain of Su Lin weighed 238 grams, minus
the dura but including the pia mater and arach-
noid. This gives a ratio to body weight of 1 : 252.
It measured 115 mm. in total length and 85 mm.
in breadth. The brain of the adult male Mei Lan
weighed 277 gi'ams, giving a ratio to body weight
of about 1 : 496. This brain was partly decom-
posed and not suitable for study.
In dorsal view the brain is almost circular in out-
line, but is somewhat acuminate anteriorly. The
olfactory bulbs project prominently beyond the
cerebrum. Posteriorly the cerebrum covers a little
less than half of the cerebellum. In lateral view
the brain is almost fiat inferiorly. The superior
outline is arched, acuminate anteriorly and trun-
cated at the posterior margin of the cerebellum.
An endocranial cast of an adult skull (fig. 143) is
much depressed in the frontal region, giving the
brain an almost triangular outline in profile view.
This reflects the degree of expansion of the dorsal
sinus system in the skull of this individual.
Rhombencephalon
Medulla oblongata
This region is short and broad, and conical in
form, tapering posteriorly. The distance from the
rear margin of the pons to the decussation of
the pyramids is 12.5 mm. The pyramids stand
out prominently, and the median ventral fissure
is correspondingly deep. The olive region is broad
and flat. Cranial nerves I X X 1 1 arise at the usual
sites. The roots of the glossopharyngeal, vagus,
and accessorius cannot be separated from one an-
other. The corpus trapezoides, lying immediately
behind the pons, is not clearly defined. From it
arise the facial and auditory nerves (VII and VIII).
The abducens (VI) arises in the angle between the
lateral border of the pyramid and the posterior
border of the corpus trapezoides.
Pons
The pons is a flattened eminence, 27 mm. in
transverse diameter. It is broadest at its poste-
rior margin and therefore somewhat trapezoidal in
outline. The basilar sulcus is very shallow. The
root of the trigeminal nerve (V) arises from the
posterolateral angle of the pons.
Cerebellum
The cerebellum is spindle-shaped in dorsal view,
almost circular in sagittal section. It measures
59 mm. in breadth by 36 mm. in length, and weighs
about 35 grams, about 15 per cent of total brain
weight. On a mid-sagittal section (fig. 146) the
cortex is extensive and richly foliated, the medulla
correspondingly small. The central gray substance
is small and stellate, the limbs of the arbor vitae
slender. A narrow, deep fastigium extends nearly
vertically from the roof of the fourth ventricle to
the central gray substance. Directly opposite the
fastigium the primary fissure divides the cerebel-
lum into anterior and posterior parts. The ante-
rior part is slightly the larger. The relations of
the remaining lobes and fissures are shown in the
illustration.
In dorsal view the anterior lobe is broad, with a
U-shaped posterior boundary marked by the pri-
mary fissure. The lunate lobule (simplex of Bolk,
1906, and Haller, 1934) is narrow and crescent-
shaped, embracing the anterior lobe from behind.
The posterior boundary is easily distinguished be-
cause the folia of the lunate are continuous across
the paramedian sulcus, whereas those of the me-
dian lobe are not. The limbs of the lunate lobule
exclude the ansiform lobule from contact with the
anterior lobe, except at the extreme anterior end
of the cerebellum. The unpaired lobulus medianus
posterior of Bolk (1906), separated from the paired
lateral lobes by the paramedian sulcus, is divided
by transverse fissures into a short median lobe
(tuber vermis), a longer pyramis, a uvula, and a
nodulus. The tuber vermis is straight as in other
arctoids.
The ansiform lobule is large and very similar to
that of the Ursidae, composed of two crura sepa-
rated by a deep and slightly S-shaped intercrural
sulcus. It hides the paraflocculus almost com-
pletely in dorsal view. The pteroid area (crus I
289
290
FIELDIAXA: ZOOLOGY MEMOIRS, VOLUME 3
Fig. 143. Endocranial east of adult female Ailuropoda (CNHM 36758). Lateral view (X 1).
of the ansiform lobule") is broad and triangular,
and continues without interruption into eras IL
Crus II is worm-like, with regular transvei-se folia,
and is faintly S-shaped. Bolk describes a second-
ary, ventrally concave loop (the "ansula") in crus II
in Ursus arctos, Thalarctos maritimus, and Felis
leo, and I found this loop well developed in two
specimens of Ursus americanus. It is absent in
the brain of Ailuropoda. Medially crus II con-
tinues without interruption into the paramedian
lobule, which descends vertically on the posterior
surface of the cerebellum, lying between the py-
ramis and the medial end of the paraflocculus.
The paraflocculus closely resembles that of the
Ursidae. It is a large U-shaped lobe composed of
regular transverse folia, giving it a worm-like ap-
pearance. The larger superior limb abuts against
the inferior end of the paramedian lobule, the
smaller and shorter inferior limb terminates against
the flocculus. The petrosal lobule, at the convex-
itj' of the U, does not protrude beyond the re-
mainder of the paraflocculus. The flocculus is a
Sulcus CTudatus
A. cerebri ant.
Fissura primaria
Cerebellum
Medulla oblongata
C<Hpus callosum
Chiasma opticum
Ventriculus tatius
Thalamus . .
Hypophysis Cwpus mamillans
Aquaeductus cerebri
CoUiculus ant.
Pons
Pedunculus cCTebri
Fig. 144. Brain of Ailuropoda, mid-sagittal section (X 1).
DAVIS: THE GIANT PANDA
291
A. ethmoidalis
A. cerebri ant.
A. cerebri med. ...^ f
i
A. communicans ant
A. chorioidea
A. carotis int.
A. communicans post
A. cerebri post.
A. cerebelli sup.-
Tractus olfactorius
N. opticus (II)
A. cerebelli inf. ant
N. facialis (VII)
N. acusticus (VIII)
A. basilaris
A. cerebelli inf.
lasma opticum
ypophysis
N. oculomotorius (III
N. trochlearis (IV)
N. trigeminus (V)
. abducens (VI)
_N. glossopharyngeus (IX)
N. vagus (X)
N. hypoglossus (XII)
N. accessorius (XI)
A. vertebralis
Fig. 145. Brain of Ailuropoda, inferior view (X 1).
small lamella wedged in between the inferior limb
of the paraflocculus and the cerebellar peduncle.
Fourth ventricle
On sagittal section this appears as a roomy
chamber, narrowing rather abruptly anteriorly and
posteriorly. Its floor is distinctly concave.
Midbrain and Thalamus
These structures were studied only on a mid-
sagittal section through the brain (fig, 144).
Midbrain
The aquaeductus cerebri (sylvii) is of almost uni-
form diameter in sagittal section, only a little larger
posteriorly than anteriorly. It lies only slightly
above the level of the fourth ventricle. The cor-
pora quadrigemina (colliculi anteriores and poste-
riores) roof over the anterior part of the aqueduct.
Each anterior quadrigeminate body is a low rounded
hillock, much broader than long. The posterior
body, on the contrary, scarcely forms an elevation.
The optic tract emerges from beneath the pyri-
form lobe of the cerebrum, closely applied to the
cerebral peduncle. In front of the tuber cinereum
the optic tract leaves the optic chiasma, from
which the optic nerves (II) arise. Mettler and
Goss commented on the small diameter of the optic
Fissura primaria
Fiss. praecentralis
Fiss. praepyramidalis
Fig. 146. Cerebellum of Ailuropoda, mid-sagittal section.
Fiss. secunda
Fiss. primaria
Lob. ant.
Lob. lunatus
S. paramed.
Lob. med.
Lob. paramed,
S. intercruralis
Lob. ansiformis
Fiss. paraflocculus
Paraflocculus
Fig. 147. Cerebellum of Ailuropoda, lateral view.
292
DAVIS: THE GIANT PANDA
293
nerves, but I find them relatively no smaller than
in a specimen of Ursus americanus.
A sagittal section through the cerebral peduncles
at the interpeduncular fossa is nearly rectangular
in outline. In inferior view the peduncles appear
as broad tracts emerging from beneath the optic
tracts and converging to disappear into the pons.
The mammillary bodies form a low rounded emi-
nence, scarcely subdivided into a paired structure,
lying in the angle between the limbs of the cere-
bral peduncles. The oculomotor nerve (III) arises
as usual from the interpeduncular fossa.
Thalamus
In mid-sagittal section the thalamus is circular,
surrounded by a rather narrow third ventricle.
Cerebrum
In mid-sagittal section the corpus callosum ap-
pears as the usual U-shaped structure, 31 mm. in
length, with a nearly straight body, a sharply bent
knee, and a slightly arched splenium. A deep sul-
cus corporis callosi separates it from the cerebral
convolutions lying directly above it.
Gyri and sulci
These were mapped by Mettler and Goss on the
brain of the panda Pan Dee. The configuration in
our specimen differs from theirs only in unimpor-
tant details. The nomenclature used here is largely
that of Papez (1929).
As in carnivores in general, the pattern of gyri
and sulci in Ailuropoda is characterized by a con-
centric series of vertical arches (the arcuate convo-
lutions) arranged around a central sylvian fissure,
with vertical furrows predominating over horizon-
tal on the whole cerebral cortex. There is a deep
sylvian fossa, with the sylvian fissure and sylvian
gyri (first arcuate convolution) hidden from view
within the fossa, as in the Ursidae (HoU, 1899;
Smith, W. K., 1933a), Procyon (Papez, 1929), and
Mustelidae (Holl, 1899). The lips of the sylvian
fossa are formed by the second arcuate convolu-
tion, composed of the anterior and posterior ecto-
sylvian gyri. The anterior ectosylvian gyrus is
more slender and lies slightly deeper than the pos-
terior. The third arcuate convolution is composed
of the anterior and posterior suprasylvian gyri.
The coronal sulcus is conspicuous, sinuous, and
oriented at an angle of about 45 to the basal plane
of the brain. It is continuous dorsally with the
lateral sulcus, as in the Ursidae. The inferior tem-
poral gyrus is represented by the inferior loop con-
necting the posterior ectosylvian and posterior
suprasylvian gyri, and is continuous with both of
these gyri. The temporal lobe of the cortex, repre-
sented by the sylvian, posterior ectosylvian, poste-
rior suprasylvian, and inferior temporal gyri (Papez,
1929), is only moderately developed as compared
with that of the dog or cat, resembling that of
the bears.
The coronal gyrus is very large and bifid inferi-
orly (this cleft was absent in the brain of Pan Dee).
In Ursus and other arctoids the inferior end of the
coronal gyrus extends forward beneath the poste-
rior sigmoid gyrus to meet the inferior end of the
anterior sigmoid gyrus. In Ailuropoda, however,
the coronal gyrus is separated from the anterior
sigmoid gyrus by the downward expansion of the
posterior sigmoid gyrus.
The postcruciate gyrus is continuous anteriorly
with the posterior sigmoid gyrus. It is well devel-
oped and subdivided by short shallow furrows, and
is considerably more extensive than the correspond-
ing gyrus in our specimen of Ursus americanus
(fig. 149). The postcruciate gyrus, together with
the coronal gyrus, represents somatic afferent area I.
The ansate sulcus, separating the postcruciate
from the posterior sigmoid area, is a short sagittal
furrow unconnected with any other furrow. In
bears the ansate may be similarly isolated (Haller,
1934, fig. 195), or it may be connected with the
lateral sulcus (fig. 148).
The sigmoid gyri, surrounding the cruciate sul-
cus, are extensive. The posterior sigmoid gyrus
(motor area I) is much expanded ventrally. The
inferior, expanded part of this gyrus corresponds
to the facial-masticatory motor area in Ursus
(Smith, W. K., 1933b). The cruciate sulcus, sep-
arating the frontal from the sigmoidal area, ex-
tends only a short distance onto the medial surface
of the hemisphere, and is not connected with any
other sulcus.
Anteriorly there is a well-developed frontal area.
It is divided into three well-marked frontal gyri:
a superior, separated from the posterior sigmoid by
the cruciate sulcus, a middle frontal, and an infe-
rior frontal (proreal). The superior frontal gyrus,
the "ursine lozenge," is about as well developed
as in the bears. The short sagittally directed pro-
real sulcus extends forward from the presylvian sul-
cus, separating the middle and inferior frontal gyri.
The lateral gyrus is broad, and is subdivided in-
to two parts by a parietal sulcus, as in Ursus. The
lateral sulcus is continuous with the postlateral
sulcus, which separates the posterior suprasylvian
gyrus from the ectolateral gyrus. The postlateral
sulcus terminates at about the level of the lower
third of the cerebrum, on both sides of the brain;
in the brain of Pan Dee it continued down into the
temporal pole, as in Ursus. In the brain of Su Lin
the ectolateral gyrus is interrupted by a short
S. lateralis
Ailuropoda melanoleuca
S. postlata^is
S. entolateralis
S. coronalis
S. postcruciatus
S. ansatus
G. frontalis sup.
S. proreus
S. suprasylvius post.
S. praesylvius
S. cruciatus
S. suprasylvius ant.
Fossa Sylvia
^M HIND LEG
FORE LEG
FACIAL AND MASTICATORY
S. entolateralis
Ursus americanus
ll ! I I 1 11 FACE
S. lateralis
FACE, TONGUE, LARYNX
S. ansatus
G. frontalis sup.
S. cruciatus
S. proreus
S. postlateralis
S. suprasylvius post
S. praesylvius
S. coronalis
S. suprasylvius ant.
Fossa Sylvia
Fig. 148. Right cerebral hemisphere of Ailuropoda and Ursus to show patterns of gyri and sulci. Lateral view. Motor
area I in Ursus mapped from Smith (1933b). Note particularly the expanded masticatory motor area in Ailuropoda.
294
DAVIS: THE GIANT PANDA
295
S. praesylvius
S. praecruciatus
S. cruciatus a\1
S. praesylvius
S. cruciatus
S. ansatus
S. coronalis
S. suprasylvius ant.
Fossa sylvia
S. suprasylvius post,
suprasylvius ant.
iylvia
suprasylvius post.
S. postlateralis
S. lateraUs g. parietalis
S. lateralis
S. parietalis
1. postlateralis
Ursus
Ailuropoda
Fig. 149. Right cerebral hemisphere of Ailuropoda and left cerebral hemisphere of Ursus americanus to show patterns
of gyri and sulci. Dorsal view.
transverse furrow in the temporal region; this sec-
ondary furrow is only indicated by a notch in the
brain of Pan Dee, and is completely absent in
Ursus.
On the medial surface of the cerebrum (fig. 150)
the cortex is divided by a deep and nearly contin-
uous furrow, paralleling the corpus callosum, into
a dorsal and a ventral system of gyri. The furrow
begins posteriorly with a very deep and nearly
vertical calcarine sulcus, which above terminates
abruptly in a short transverse furrow. Behind the
calcarine sulcus lies the broad lingual gyrus, cleft
by a postcalcarine sulcus and behind this by a para-
calcarine sulcus, both of which parallel the cal-
carine sulcus. A short intercalary sulcus connects
anteriorly with a long cingular sulcus, from which
three short lateral furrows go off at right angles.
Anteriorly, the cruciate sulcus is continued into a
U-shaped rostral sulcus. T:ie genual sulcus is a
short diagonal fissure behind the rostral sulcus.
The system of sulci on the medial surface of the
rostral region is much simpler than in Ursus (see
also Smith, W. K., 1933a, fig. 6).
The inferior end of the calcarine sulcus is con-
tinuous with a well-developed sulcus on the infe-
rior surface of the brain, running laterad behind
the rhinal fissure. According to Elliot Smith (1902)
this sulcus is fully developed only in bears (see also
Smith, W. F., 1933a, fig. 8), and was called by him
the "ursine sulcus." It is as well developed in
Ailuropoda as in the bears.
The parasplenial gyrus is remarkably broad. It
is bounded inferiorly by the corpus callosum, pos-
teriorly by the calcarine sulcus, and superiorly by
the intercalary and cingular sulci. Anteriorly it
continues without interruption into the cingular
296 FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
AUuropoda melanoleuca
S. verticalis
S. cingularis
S. intercalaris
S. suprasplenialis
S. cniciatus
S. rostralis
S. postcalcarinus
S. paracalcarinus
S. calcarinus
S. genualis
S. lu^nus
Ursus americantis
S. verticalis
S. intercalaris
suprasplenialis
S. rostralis
S. calcarinus
paracalcarinus
S. ursinus
Fig. 150. Medial surface of right cerberal hemisphere of AUuropoda and Ursus to show patterns of gyri and sulci.
gyrus, which is also notably broad. The straight
and subcallosal gyri are poorly marked. The supra-
splenial gyrus bears a short, nearly vertical su-
prasplenial sulcus instead of the longitudinal one
usually present in carnivores. The middle parietal
gyrus is much longer than in Ursus. Because of
the short distance that the cruciate sulcus extends
onto the medial surface of the hemisphere, the
middle parietal gyrus is continuous with the supe-
rior frontal gyrus.
Central Olfactory Structures
The olfactory brain of AUuropoda is much re-
duced compared with the corresponding structures
in a brain of Ursus americanus. The bulbs are
relatively smaller, and the olfactory stalks slender.
The olfactory bulbs are ovate structures, about
16 mm. in length, lying anterior to the cerebrum.
The olfactory tracts are prominent but slender.
Each divides posteriorly into lateral and medial
parts. The lateral olfactory tract is much the
larger. It is a rope-like structure that diverges
from the midline as it runs posteriorly; it termi-
nates in the pyriform lobe. The medial olfactory
tract is a short flat band that separates from the
lateral tract and runs posteriorly and medially to
the olfactory tubercle. The olfactory tubercle is
1
DAVIS: THE GIANT PANDA
297
a low eminence, perforated by numerous holes for
blood vessels, lying just anterior and medial to the
tip of the pyriform lobe. Between the olfactory
tubercle and the optic tract is a rather broad diag-
onal band of Broca, the lateral end of which dis-
appears beneath the pyriform lobe.
Discussion of Brain
Comparative studies of the brain in the Carni-
vora have dealt almost entirely with the pattern
of the gyri and sulci in the cerebral cortex. The
morphology of these structures was compared by
Krueg (1880), Mivart (1885b), Holl (1889), Klatt
(1928), Papez (1929) and Haller (1934). Motor
areas in the cortex of Ursus were mapped by W. K.
Smith (1933b), and both motor and sensory areas
in Procyon by Welker and Seidenstein (1959) and
in Canis most recently by Pinto Hamuy, Bromiley
and Woolsey (1956).
The brain of Procyon has been figured by Klatt,
Papez, and Welker and Seidenstein, that of Nasua
by Klatt, and of Ailurus by Flower (1870) and
Klatt. Bear brains have been figured by Mivart,
Papez, W. K. Smith (1933a), Haller, and others.
I had the following arctoid brains available for
comparison: Bassariscus astutus (1), Procyon lotor
(3), Nasua narica (1), Ailurus fulgens (1), Ursus
americanus (2).
The question of whether the sulci demarcate
physiological subdivisions of the cortex or are mere
artifacts resulting from expansion of the cortex is
of considerable importance, since it is unlikely that
the brains of more than a few species will ever be
studied experimentally in the living state. This
question has been much disputed (Haller, 1934).
The work of Welker and Seidenstein indicates that
at least in the Carnivora the sulci do delimit true
physiological subdivisions, the correspondence in
Procyon extending down to such small anatomical
units as the individual digits. They found a faith-
ful relation maintained despite individual varia-
tions in the location and orientation of the sulci.
Of similar interest is the question of whether
there is a correlation between degree of receptor
specialization and degree of cortical elaboration.
Such a correlation has been found for every exam-
ple of a highly specialized function that has been
checked experimentally (reviewed by Welker and
Seidenstein, 1959), and we may therefore assume
with some confidence that similar correlations exist
in animals where experimental verification is im-
possible.
The pattern of gyri and sulci is remarkably uni-
form in all canids (Mivart, 1885b; Klatt, 1928),
and more primitive than that of the Procyonidae
and Ursidae. The Procyonidae and Ursidae, in
turn, have a common pattern. The pattern in
Ailurus is more primitive than in Procyon and
Nasua, but definitely represents the procyonid-
ursid type (Klatt).
In the procyonids and bears the sigmoidal (mo-
tor I) and coronal and postcruciate (somatic affer-
ent) areas of the cortex are greatly expanded, and
elaboration of these areas is associated with a cor-
responding elaboration of the motor and sensory
functions (Smith, W. K., 1933b; Welker and Sei-
denstein, 1959). The morphological result of this
expansion is that (1) the superior end of the sylvian
fossa tends to be crowded posteriorly, (2) the syl-
vian gyri (first arcuate convolution) are crowded
into the sylvian fossa, where they are hidden from
view, and (3) the postcruciate area is considerably
divided up by secondary fissures, especially in the
Procyonidae. On the medial surface of the hemi-
sphere the cruciate sulcus fails to meet the cingular
sulcus, at least in Procyon, Ailurus, and the Ursi-
dae. These two sulci meet in all canids.
The bears and procyonids differ in a few impor-
tant respects, and in several minor details sum-
marized briefly by Mettler and Goss. The frontal
area of the cortex is relatively larger in bears, and
the superior frontal gyrus appears on the surface
as a well-developed "ursine lozenge," a structure
that is rudimentary in procyonids and absent in
other carnivores. The procyonid brain is notable
for the great expansion of the postcruciate area
(the central part of somatic afferent area I). As
a result of this expansion the continuity of the
coronal-lateral sulcus is broadly interrupted, where-
as in the Ursidae these two sulci are continuous as
in other arctoids. Welker and Seidenstein (1959)
have showti that this expanded part of somatic
afferent area I is devoted to the hand in Procyon.
In the bears the lateral gyrus is divided longitudi-
nally by a parietal sulcus (often indicated in dogs),
whereas in procyonids this gyrus is narrower and
lacks the parietal sulcus.
Gross differences in the cerebral cortex between
the Canidae on the one hand, and the Procyonidae
and Ursidae on the other, are attributable almost
entirely to expansion of three areas in the procy-
onid-bear brain. These are (1) the postcruciate-
coronal area, (2) the sigmoidal area, and (3) the
frontal area. These cannot be attributed to dif-
ferences in brain size, since the procyonids are con-
siderably smaller than large dogs. Experimental
studies have shown, on the contrary, that elabora-
tion of the first two of these areas is associated with
elaboration of manual and prehensile functions in
procyonids and bears.
In Ailuropoda the pattern of gyri and sulci agrees
closely with that of the Ursidae. Mettler and Goss
298
FIELD lANA: ZOOLOGY MEMOIRS, VOLUME 3
state that the arrangement in Ailuropoda "is so
similar to what is seen in the bears that one is
forced to rely on small variations from the ursine
pattern to detect any differences in the brain."
The brain of Su Lin differs in minor details from
the brain of Pan Dee as described and figured by
Mettler and Goss, but confirms the close similarity
in gross brain structure between the giant panda
and the bears. The cortex of Ailuropoda differs
in two points that seem to be of importance: (1)
The postcruciate area is considerably larger than
in Ursus. A similar, though even more extensive
elaboration of this area is associated with elabo-
ration of sensory functions of the hand in Procyon
(Welker and Seidenstein). It is reasonable to as-
sume a similar correlation in Ailuropoda. (2) The
inferior end of the posterior sigmoid gyrus is con-
siderably larger than in Ursus. This is the facial-
masticatory motor area in Ursus (Smith, W. K.,
1933b), and its elaboration in Ailuropoda is asso-
ciated with elaboration of the masticatory func-
tion. The motor area for the fore limb does not
appear to be any larger than in Ursus.
Thus the two elements of major adaptive speciali-
zation in Ailuropoda (the hand and the masticatory
apparatus) are both associated with elaboration of the
corresponding areas of the cerebral cortex.
The gross structure of the cerebellum offers little
of interest within the Carnivora. Eight carnivores,
including three arctoids (Canis familiaris, Ursus
arctos, Thalarctos maritimus) were included in the
material used by Bolk (1906). In general, the cere-
bellum is better developed in bears than in Canis.
This is particularly evident in crus II of the ansi-
form lobule, in which a secondary loop (the an-
sula) is present in bears. The ansula is absent in
Ailuropoda and the Procyonidae.
Among the Carnivora, the cerebellum is largest
in the Ursidae (15.8-16.3 per cent of total brain
weight in three individuals), smallest in the Cani-
dae (average 9.5 per cent in 16 domestic dogs)
(Putnam, 1928). No values are available for any
procyonid. My figure for Ailuropoda (15 per cent)
is very similar to that for the bears.
Conclusions
1. Gross differences in brain structure among arc-
toid carnivores involve chiefly the cerebral cortex.
2. In the Canidae the cerebral cortex is less spe-
cialized than in the Procyonidae and Ursidae.
3. In the Procyonidae and Ursidae the cerebral
cortex has been modified by expansion of three
areas: the sigmoidal, coronal and postcruciate, and
frontal. The first two are associated with enhanced
prehensile and tactile functions of the fore limb in
raccoons and bears.
4. In gross structure the brain of Ailuropoda
agrees closely with the brain of the Ursidae in all
respects.
5. The postcruciate gyrus (somatic afferent area
for the fore limb) and the inferior end of the pos-
terior sigmoid gyrus (masticatory motor area) are
larger in Ailuropoda than in Ursus.
II. CRANIAL NERVES
A^. Opticus (II) (fig. 151)
The optic nerve emerges from the optic foramen,
to pursue a faintly S-shaped course to the eye ball.
It has a diameter of about 2.5 mm., and its length
from the optic foramen to the back of the eye ball
is 50 mm.
A'^. Oculomotorius (III) (fig. 151)
The oculomotor nerve is the most medial of the
nerves passing out of the orbital fissure. Just be-
fore reaching the base of the rectus superior muscle
it divides into superior and inferior branches. The
smaller superior branch passes along the lateral
border of the rectus superior, supplying that mus-
cle and giving off a fine twig to the levator palpe-
brae superioris.
The inferior branch passes forward between the
rectus superior and the retractor oculi, then be-
neath the optic nerve. At about the middle of the
optic nerve it gives off a branch to the rectus me-
dialis, a branch to the rectus inferior, then the
Radix brevis ganglii ciliaris, and is itself continued
as a branch to the oblique inferior.
N. Trochlearis (IV) (fig. 151)
The trochlear nerve is the most dorsal of the
nerves passing out of the orbital fissure. It passes
forward above the rectus superior and levator pal-
pebrae superior to the dorsal border of the superior
oblique. The nerve enters the latter muscle at
about its middle.
A^. Trigeminus (V)
N. Ophthalmicus (Trigeminus 1)
The ophthalmic nerve emerges from the skull
through the orbital fissure, situated within the
ophthalmic vein. It emerges from the vein at the
posterior third of the orbit, where the vein breaks
up into its terminal branches. The ophthalmic
nerve has only two main branches, the frontal and
the nasociliary.' The nerve separates into these
branches at the semilunar ganglion.
1. N. frontalis (fig. 152) is slightly smaller than
the nasociliary. It accompanies the frontal artery
and superior orbital vein over the dorsal surface of
' The lacrimal branch of the human ophthalmic forms a
part of the maxillary nerve in carnivores (see p. 30).
DAVIS: THE GIANT PANDA
299
Biilbus oculi
R. palpebralis iiif
R. palpebralis sup.
N. infratrochlearis
N. TROCHL.EARIS (IV)
N. m. levator palpebrae sup
Nn. ciliares longi
N. ethmoidalis
Foramen ethmoidalis
N. opticus
Foramen opticum H-i;
R. inf. , n. oculomotori
R. sup., n. oculomotorius
Radix sympathica ganglii ciliari
N. nasociliaris-
R. periorbiti
N. OCULOMOTORIUS (III) \
,N. m. obliquus inf.
Nn. ciliares breves
Ganglion ciliare
Radix brevis ganglii ciliaris
N. m. rectus inf.
N. m. rectus med.
R. recurrens
Rr. post, ganglii ciliaris
Nn. m. retractor oculi inf.
N. m. retractor oculi med.
N. m. retractor oculi sup.
N. m. retractor oculi lat.
R. m. rectus lat.
R. m. retractor oculi lat.
R. plexus ophthalmicus
N. sympathicus, plexus cavernosus
iss. orbitalis + Foramen rotundum
N. ABDUCENS (VI)
Fig. 151. Nerves of right orbit of Ailuropoda, dorsal view (semi-diagrammatic). The frontal, lacrimal, and zygomatic
nerves have been removed.
M. obliquus superior, all three structures piercing
the dorsal wall of the periorbita at about the mid-
dle of the orbit and passing together into the supra-
orbital space.
Rr. periorbiti, the first branches of the frontal,
are a pair of delicate twigs arising from the fron-
tal as it emerges from the orbital fissure. They
pass to the dorsal wall of the periorbita. At their
bases the periorbital branches receive a sympa-
thetic twig from the plexus cavernosus.
The frontal nerve breaks up into three subequal
terminal branches as it pierces the periorbita. N.
supratrochlearis, the first to come off and the
most laterally situated, passes forward above the
pulley of the superior oblique muscle, emerging
onto the forehead immediately above the eye.
N. supraorbitalis runs immediately in front of
the postorbital ligament, continuing onto the fore-
head above and behind the eye. R. frontalis,
the most medial of the terminal branches, runs
300
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
R. frontalis
N. supraorbitaIis\
N. supratrochlearis
Nn. zygomatid
N. lacrimalis
Ganglion sphenopalatinum
Nn. infraorbitales
FORAMEN INFRAORBITALe/ n. nasopalatinus
FORAMEN
SPHENOPALATINUM
R. nasalis post. med.
R. nasalis post. lat.
CANALIS PHARYNGIS
Nn. palatini ant.
Nn. sphenopalatini
Nn. alveolares sup. post.
Rr. periorbiti
\N. nasociliaris (cut)
XT
N. canalis pterygoidei
N. ophthalmicus (Vi)
N. nasociliaj
N. frontalis
Nn. zyg. & lac.
FISSURA ORBITALIS
& FORAMEN ROTUNDUM
glandulae orbitalis
'T^ \ Nn. alveolares sup. post.
/' I N. maxillaris (V2)
N. petros. sup. maj.
Fig. 152. Maxillary nerve (V2) and frontal branch of ophthalmic of Ailuropoda. Dorsal view.
onto the forehead beside the supraorbital nerve,
passing into the frontal area above the eye.
2. N. nasociliaris runs forward, at first lying
on the retractor muscles of the eye, then passing
between the superior rectus and the optic nerve.
The nasociliary terminates, after crossing over the
optic nerve, by dividing into the infratrochlear and
ethmoidal nerves. The nasociliary nerve gives rise
to the following branches:
(a) Nn. ciliares longi, two in number, come
off before the nasociliary reaches the level of the
optic foramen. These arise by three roots, with a
fourth root (Radix sympathicus ganglii cili-
aris) coming from the plexus cavernosus. Be-
yond the optic foramen the two nerves separate.
One passes to the medial side of the optic nerve,
while the other remains on its lateral side, joining
the short ciliary nerves at the level of the ciliary
ganglion and continuing forward with them. As
it approaches the ciliary ganglion, the lateral long
ciliary nerve gives off the Radix longa ganglii
ciliaris.
(b) N. infra trochlearis, the smaller of the two
terminal branches, passes forward under the pulley
of the obliquus superior muscle. It divides into
superior and inferior palpebral branches directly
beneath the pulley.
(c) N. ethmoidalis arches back around the
base of the obliquus superior, to enter the eth-
moidal foramen.
Ganglion ciliare is a small, triangular, much
flattened body situated on the lateral side of the
optic nerve about 20 mm. behind its entrance into
the eye ball. Roots: (a) The short root is a short,
heavy branch derived from the branch of the ocu-
lomotor supplying the obliquus inferior, (b) The
DAVIS: THE GIANT PANDA
301
long root arises from the more lateral of the
two long ciliary nerves, (c) The sympathetic root,
which comes from the plexus cavernosus, accom-
panies the long ciliary nerve and is macroscopically
inseparable from it through most of its course.
Branches: (a) Several Nn. ciliares breves leave
the anterior end of the ganglion and accompany
the long ciliary nerve to the eye ball, (b) Two
branches leaving the posterior end of the ganglion
supply the retractor oculi. (c) A slender recurrent
branch passes on the optic nerve back to the optic
foramen.
N. maxillaris (Trigeminus 2)
The maxillary nerve (fig. 152) emerges from the
skull through the combined orbital fissure and fora-
men rotundum. The maxillary nerve lies in the lat-
eral part of the foramen, and is separated from the
ophthalmic nerve by the periorbita. It passes an-
teriorly along the inferior border of the periorbita,
giving off numerous branches in the suborbital
space, and terminating near the infraorbital fora-
men by breaking up into several infraorbital neives.
The branches of the maxillary nerve are :
1. N. meningeus medius can be seen as a
delicate twig running along the posterior border
of the anterior branch of the middle meningeal
artery. It arises from the common trunk of the
lacrimal and zygomatic nerves just before that
trunk enters the orbital fissure.
2. The trunk for the laci'imal and zygomatic
nerves arises from the maxillary inside the skull.
The common trunk of the two nerves passes for-
ward inside the periorbita, dividing into lacrimal
and zygomatic components at the posterior third
of the orbit. N. lacrimalis, the most ventral
component, passes forward to the lacrimal gland.
Twigs from this nerve leave the orbit at the outer
angle of the eye, passing across the zygoma to
anastomose with the zygomatic branch of the fa-
cial nerve. Nn. zygomatici, two in number,
leave the orbit by piercing the orbital ligament.
They anastomose with temporal branches of the
facial nerve in the temporal region.
3. Nn. alveolares superiores posteriores
arise by five roots from the lateral side of the max-
illary nerve as it lies in the suborbital space. These
roots unite to form a loose plexus that extends
nearly from the orbital fissure to the infraorbital
foramen, and twigs arising from this plexus ramify
to the minute foramina in the alveolar prominence;
thus they supply the molar teeth exclusively. The
most anterior twig passes into the infraorbital
foramen.
4. Nn. sphenopalatini arise by four roots
from the medial side of the maxillary nerve in the
posterior half of the orbit. These roots unite just
before they enter the sphenopalatine ganglion.
The ganglion sphenopalatinum is situated just
outside the opening of the pharyngeal canal, and
is quite inconspicuous. The following branches
arise from it: (a) N. palatinus posterior is a slen-
der twig arising from the posterior end of the gan-
glion. It passes backward, joining the A. canalis
pterygoidei and accompanying it through the notch
in the outer border of the vertical pterygoid plate
to the soft palate, (b) N. canalis pterygoidei
also arises from the posterior end of the ganglion.
It entei-s a small foramen situated directly below
the optic foramen, through which it passes to the
roof of the pharynx, (c) Nn. palatini anteriores
arise from the anterior end of the ganglion. They
enter the pterygopalatine canal, emerging onto the
hard palate through both the greater and the lesser
palatine foramina, (d) N. nasopalatinus, the
largest nerve arising from the ganglion, immedi-
ately joins the sphenopalatine artery and passes
with it into the sphenopalatine foramen.
5. Nn. infraorbitales, to the number of three,
are the terminal branches of the maxillary nerve.
They accompany the infraorbital artery through
the infraorbital foramen, five main branches emerg-
ing to ramify over the side of the face. Rr. alveo-
lares superiores anteriores from these branches
pass, without the intervention of a plexus, into the
minute foramina situated just above the gum line;
thus they supply the premolar, canine, and incisor
teeth.
N. mandibularis (Trigeminus 3)
The mandibular nerve (fig. 153) is smaller than
the maxillary division of the trigeminus. It emerges
from the skull through the foramen ovale as a large
trunk, accompanied on its medial side by the much
smaller masticator nerve.
The ganglion oticum is situated on the poste-
rior (lateral) surface of the nerve.
Four nerves arise from the mandibular proximal
to the otic ganglion, before the nerve divides into
anterior and posterior parts:
1. N. spinosus comes off at the mouth of the
foramen. It is a slender recurrent twig that passes
back through the foramen ovale.
2. N. buccinatorius also arises at the mouth
of the foramen. It passes forward between the
heads of the external pterygoid muscle, across (ex-
ternal to) the inferior alveobuccal gland, which it
supplies, and on into the cheek. It communicates
with terminal twigs of the buccal branch of the
facial nerve on the cheek.
3. N. pterygoideus internus is a twig arising
from the ventral side of the mandibular at the
302
FIELDIANA: ZOOLOGY MEMOIRS, VOLUME 3
mouth of the foramen. It runs forward across the
posterior end of the ventral head of the external
pterygoid muscle into the internal pterygoid muscle.
4. N. pterygoideus externus arises at the an-
gle between the two divisions of the mandibular.
It accompanies the buccinator nerve to the exter-
nal pterygoid muscle, which it supplies.
The posterior division of the mandibular passes
laterad between the external pterygoid muscle and
the medial end of the mandibular condyle. Just
beyond the medial end of the condyle it breaks
up into its terminal branches. Near this point it
gives off a slender root that passes back to the otic
ganglion.
The branches arising from the posterior division
are:
5. N. lingualis, the first of the terminal
branches, passes forward and downward between
the external and internal pterygoid muscles. It is
joined, at an acute angle, by the chorda tympani at
the posterior border of the internal pterygoid.
At the anterior border of the internal pterygoid the
lingual nerve lies between that muscle and the my-
lohyoid. It then passes between the mylohyoid
and the sublingual gland, which it supplies, into
the tongue. Here, immediately after crossing ven-
trad of the duct of the submaxillary gland, it breaks
up into its several terminal branches. N. sublin-
qualis, the most dorsal of these terminal branches,
runs forward to supply the sublingual gland and
the mucous membrane on the ventral side of the
tongue.
6. N. alveolaris inferior accompanies the in-
ferior alveolar artery forward between the internal
pterygoid muscle and the lower part of the deep
temporal muscle. The nerve lies above the artery
as they pass together into the mandibular fora-
men. The terminal branches emerge from the
mandible through the mental foramina.
7. N. mylohyoideus arises beside the inferior
alveolar nerve. It accompanies the inferior alveo-
lar as far as the anterior border of the internal
pterygoid muscle, then separates from the nerve
to arch around the muscle and pass into the mylo-
hyoid. Twigs arising from the nerve just before it
enters the mylohyoid supply the digastric.
8. N. auriculotemporalis, the largest branch
of the mandibular nerve, arises from the mandib-
ular by a single root, with several delicate twigs
coming from the otic ganglion. There is no rela-
tion with the middle meningeal artery, which en-
ters the orbital fissure and hence is associated with
the maxillary division of the trigeminus. The au-
riculotemporal nerve passes laterad between the
internal pterygoid muscle and the condyle of the
mandible, then across the neck of the mandibular
condyle, lying first ventrad, then mesad of the in-
ternal maxillary artery. It breaks up into its ter-
minal branches near the lateral end of the condyle.
The auriculotemporal gives off the following
branches: (a) R, articularis, a slender branch aris-
ing near its base, passes to the medial end of the
mandibular articulation, (b) N. meatus audi-
torii externi runs dorsad to the base of the au-
ditory meatus, (c) Rr. parotidei are represented
by several fine twigs that pass into the substance
of the parotid gland, (d) R. auricularis ante-
rior, a single large branch arising just distad of
the nerve to the external auditory meatus, passes up
along the anterior side of the pinna, (e) Rr. tem-
porales superficiales, the final terminal branches
of the auriculotemporal, pass forward and upward
onto the lower part of the anterior temporal region.
A stout communicating branch arising from the
common trunk of the superficial temporal anasto-
moses with the zygomaticotemporal branch of the
facial nerve, and some of the twigs of the super-
ficial temporal terminate by anastomosing with
the zygomatic ramus of the zygomaticotemporal
branch.
9. The anterior division of the mandibular, N.
masticatorius (fig. 153), runs laterad above (deep
to) the dorsal head of the external pterygoid mus-
cle, giving off a stout root to the otic ganglion
along the way. As it lies above the muscle it di-
vides into anterior and posterior branches. The
anterior branch, N. temporalis profundus an-
terior, ramifies in the deep temporal muscle, me-
sad of the coronoid process of the mandible. The
posterior branch passes into the temporal muscle
behind the coronoid process, where it divides into
the posterior deep temporal and masseteric nerves.
N. temporalis profundus posterior ramifies in
the temporal musculature posterior to the coronoid
process. N. massetericus arches around behind
the coronoid process into the masseteric muscle,
where it ramifies.
N. abducens (VI) is the most ventral of the
nerves passing out of the orbital fissure. It passes
forward on the retractor oculi, then perforates the
inferior division of the retractor oculi to reach the
medial surface of the rectus lateralis, in which it
terminates.
N. facialis (VII)
The facial nerve (fig. 153) enters the internal
auditory meatus in company with the auditory
nerve and the internal auditory artery, and leaves
the skull through the stylomastoid foramen, in
company with the auricular branch of the vagus.
These two nerves pass laterad and ventrad to-
gether, situated in a conspicuous groove, beneath
N. buccinatorius (Vs)
N. lingualis (Vs)
N. massetericus (V^)
N. alveolaris inf.
N. temp. prof, post,
N. mylohyoideus
N. auriculo-
temporalis (V;
FORAMEN
POSTGLENOIDEUM
N. meatus acustici ext. (V3)
I^. anastomoticus
R. parotideus
N. buccalis
N. zygomaticotemporalis
R. digastricus
N. facialis (VII)
N. auricularis int.
R. auricularis of vagus
N. auricularis post
N. temp. prof. ant. (V4)
N. pter. int. (V4)
N. massetericus (V4)
N. pter. ext. (V4)
Ganglion oticum
FORAMEN OVALE
N. spinosus (Vg)
N. petros. superf. min.
R. tensor tympani (VII)
N. chorda tympani
FORAMEN LACERUM MED.
Bulla
FORAMEN LACERUM POST.
N. glossopharyngeus (IX)
FORAMEN CONDYLOIDEUM
f- Ganglion cervicale sup.
Ganglion nodosum
N. accessorius (XI)
Fig. 153. Posterior cranial nerves of Ailurop